Initial Drupal 11 with DDEV setup

web/core/modules/block/tests/fixtures/update/add-menu-block-with-zero-depth.php

@@ -0,0 +1,26 @@
+<?php
+
+/**
+ * @file
+ * Adds a menu block with a `depth` setting of 0.
+ */
+
+use Drupal\Core\Database\Database;
+
+$connection = Database::getConnection();
+
+$data = $connection->select('config')
+  ->condition('name', 'block.block.olivero_account_menu')
+  ->fields('config', ['data'])
+  ->execute()
+  ->fetchField();
+$data = unserialize($data);
+// Change the depth setting to 0, which the update hook should change to NULL.
+// @see system_post_update_set_menu_block_depth_to_null_if_zero().
+$data['settings']['depth'] = 0;
+$connection->update('config')
+  ->condition('name', 'block.block.olivero_account_menu')
+  ->fields([
+    'data' => serialize($data),
+  ])
+  ->execute();

web/core/modules/block/tests/modules/block_test/block_test.info.yml

@@ -0,0 +1,7 @@
+name: 'Block test'
+type: module
+description: 'Provides test blocks.'
+package: Testing
+version: VERSION
+dependencies:
+  - drupal:block

web/core/modules/block/tests/modules/block_test/block_test.routing.yml

@@ -0,0 +1,7 @@
+block_test.test_multiple_forms:
+  path: '/test-multiple-forms'
+  defaults:
+    _controller: '\Drupal\block_test\Controller\TestMultipleFormController::testMultipleForms'
+    _title: 'Multiple forms'
+  requirements:
+    _access: 'TRUE'

web/core/modules/block/tests/modules/block_test/block_test.services.yml

@@ -0,0 +1,6 @@
+services:
+  block_test.multiple_static_context:
+    class: Drupal\block_test\ContextProvider\MultipleStaticContext
+    arguments: ['@current_user', '@entity_type.manager']
+    tags:
+      - { name: 'context_provider' }

web/core/modules/block/tests/modules/block_test/config/install/block.block.test_block.yml

@@ -0,0 +1,17 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - block_test
+  theme:
+    - stark
+id: test_block
+theme: stark
+region: '-1'
+weight: 0
+plugin: test_html
+settings:
+  label: 'Test HTML block'
+  label_display: hidden
+  provider: block_test
+visibility: {  }

web/core/modules/block/tests/modules/block_test/config/schema/block_test.schema.yml

@@ -0,0 +1,10 @@
+block.settings.test_block_instantiation:
+  type: block_settings
+  label: 'Test block instantiation settings'
+  mapping:
+    display_message:
+      type: string
+      label: 'Message text'
+
+condition.plugin.baloney_spam:
+  type: condition.plugin

web/core/modules/block/tests/modules/block_test/src/BlockRenderAlterContent.php

@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test;
+
+use Drupal\Core\Render\Element\RenderCallbackInterface;
+
+/**
+ * Implements a trusted preRender callback.
+ */
+class BlockRenderAlterContent implements RenderCallbackInterface {
+
+  /**
+   * Render API callback: Alters the content of a block.
+   *
+   * This function is assigned as a #pre_render callback.
+   */
+  public static function preRender(array $build) {
+    $build['#prefix'] = 'Hiya!<br>';
+    return $build;
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/ContextProvider/MultipleStaticContext.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\ContextProvider;
+
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Plugin\Context\ContextProviderInterface;
+use Drupal\Core\Plugin\Context\EntityContext;
+use Drupal\Core\Session\AccountInterface;
+
+/**
+ * Sets multiple contexts for a static value.
+ */
+class MultipleStaticContext implements ContextProviderInterface {
+
+  /**
+   * The current user.
+   *
+   * @var \Drupal\Core\Session\AccountInterface
+   */
+  protected $account;
+
+  /**
+   * The user storage.
+   *
+   * @var \Drupal\user\UserStorageInterface
+   */
+  protected $userStorage;
+
+  /**
+   * Constructs a new MultipleStaticContext.
+   *
+   * @param \Drupal\Core\Session\AccountInterface $account
+   *   The current user.
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity type manager.
+   */
+  public function __construct(AccountInterface $account, EntityTypeManagerInterface $entity_type_manager) {
+    $this->account = $account;
+    $this->userStorage = $entity_type_manager->getStorage('user');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getRuntimeContexts(array $unqualified_context_ids) {
+    $current_user = $this->userStorage->load($this->account->id());
+
+    $context1 = EntityContext::fromEntity($current_user, 'User A');
+    $context2 = EntityContext::fromEntity($current_user, 'User B');
+
+    $cacheability = new CacheableMetadata();
+    $cacheability->setCacheContexts(['user']);
+
+    $context1->addCacheableDependency($cacheability);
+    $context2->addCacheableDependency($cacheability);
+
+    return [
+      'userA' => $context1,
+      'userB' => $context2,
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getAvailableContexts() {
+    return $this->getRuntimeContexts([]);
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Controller/TestMultipleFormController.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Controller;
+
+use Drupal\Core\Controller\ControllerBase;
+use Drupal\Core\Form\FormState;
+
+/**
+ * Controller for block_test module.
+ */
+class TestMultipleFormController extends ControllerBase {
+
+  public function testMultipleForms() {
+    $form_state = new FormState();
+    $build = [
+      'form1' => $this->formBuilder()->buildForm('\Drupal\block_test\Form\TestForm', $form_state),
+      'form2' => $this->formBuilder()->buildForm('\Drupal\block_test\Form\FavoriteAnimalTestForm', $form_state),
+    ];
+
+    // Output all attached placeholders trough
+    // \Drupal\Core\Messenger\MessengerInterface::addMessage(), so we can
+    // see if there's only one in the tests.
+    $post_render_callable = function ($elements) {
+      $matches = [];
+      preg_match_all('<form\s(.*?)action="(.*?)"(.*)>', (string) $elements, $matches);
+
+      $action_values = $matches[2];
+
+      foreach ($action_values as $action_value) {
+        $this->messenger()->addStatus('Form action: ' . $action_value);
+      }
+      return $elements;
+    };
+
+    $build['#post_render'] = [$post_render_callable];
+
+    return $build;
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Form/FavoriteAnimalTestForm.php

@@ -0,0 +1,48 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Form that performs favorite animal test.
+ *
+ * @internal
+ */
+class FavoriteAnimalTestForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'block_test_form_favorite_animal_test';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['favorite_animal'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Your favorite animal.'),
+    ];
+
+    $form['submit_animal'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Submit your chosen animal'),
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->messenger()->addStatus($this->t('Your favorite animal is: @favorite_animal', ['@favorite_animal' => $form['favorite_animal']['#value']]));
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Form/TestForm.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Form;
+
+use Drupal\Core\Form\FormBase;
+use Drupal\Core\Form\FormStateInterface;
+
+/**
+ * Form that performs base block form test.
+ *
+ * @internal
+ */
+class TestForm extends FormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getFormId() {
+    return 'block_test_form_test';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildForm(array $form, FormStateInterface $form_state) {
+    $form['email'] = [
+      '#type' => 'email',
+      '#title' => $this->t('Your .com email address.'),
+    ];
+
+    $form['show'] = [
+      '#type' => 'submit',
+      '#value' => $this->t('Submit'),
+    ];
+
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function validateForm(array &$form, FormStateInterface $form_state) {
+    if (!str_contains($form_state->getValue('email'), '.com')) {
+      $form_state->setErrorByName('email', $this->t('This is not a .com email address.'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitForm(array &$form, FormStateInterface $form_state) {
+    $this->messenger()->addStatus($this->t('Your email address is @email', ['@email' => $form['email']['#value']]));
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Hook/BlockTestHooks.php

@@ -0,0 +1,73 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Hook;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Hook\Attribute\Hook;
+
+/**
+ * Hook implementations for block_test.
+ */
+class BlockTestHooks {
+
+  /**
+   * Implements hook_block_alter().
+   */
+  #[Hook('block_alter')]
+  public function blockAlter(&$block_info): void {
+    if (\Drupal::state()->get('block_test_info_alter') && isset($block_info['test_block_instantiation'])) {
+      $block_info['test_block_instantiation']['category'] = 'Custom category';
+    }
+  }
+
+  /**
+   * Implements hook_block_view_BASE_BLOCK_ID_alter().
+   */
+  #[Hook('block_view_test_cache_alter')]
+  public function blockViewTestCacheAlter(array &$build, BlockPluginInterface $block): void {
+    if (\Drupal::state()->get('block_test_view_alter_suffix') !== NULL) {
+      $build['#attributes']['foo'] = 'bar';
+    }
+    if (\Drupal::state()->get('block_test_view_alter_append_pre_render_prefix') !== NULL) {
+      $build['#pre_render'][] = '\Drupal\block_test\BlockRenderAlterContent::preRender';
+    }
+  }
+
+  /**
+   * Implements hook_block_view_BASE_BLOCK_ID_alter().
+   *
+   * @see \Drupal\Tests\block\Kernel\BlockViewBuilderTest::testBlockViewBuilderCacheTitleBlock()
+   */
+  #[Hook('block_view_page_title_block_alter')]
+  public function blockViewPageTitleBlockAlter(array &$build, BlockPluginInterface $block): void {
+    $build['#cache']['tags'][] = 'custom_cache_tag';
+  }
+
+  /**
+   * Implements hook_block_build_BASE_BLOCK_ID_alter().
+   */
+  #[Hook('block_build_test_cache_alter')]
+  public function blockBuildTestCacheAlter(array &$build, BlockPluginInterface $block): void {
+    // Test altering cache keys, contexts, tags and max-age.
+    if (\Drupal::state()->get('block_test_block_alter_cache_key') !== NULL) {
+      $build['#cache']['keys'][] = \Drupal::state()->get('block_test_block_alter_cache_key');
+    }
+    if (\Drupal::state()->get('block_test_block_alter_cache_context') !== NULL) {
+      $build['#cache']['contexts'][] = \Drupal::state()->get('block_test_block_alter_cache_context');
+    }
+    if (\Drupal::state()->get('block_test_block_alter_cache_tag') !== NULL) {
+      $build['#cache']['tags'] = Cache::mergeTags($build['#cache']['tags'], [\Drupal::state()->get('block_test_block_alter_cache_tag')]);
+    }
+    if (\Drupal::state()->get('block_test_block_alter_cache_max_age') !== NULL) {
+      $build['#cache']['max-age'] = \Drupal::state()->get('block_test_block_alter_cache_max_age');
+    }
+    // Test setting #create_placeholder.
+    if (\Drupal::state()->get('block_test_block_alter_create_placeholder') !== NULL) {
+      $build['#create_placeholder'] = \Drupal::state()->get('block_test_block_alter_create_placeholder');
+    }
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestAccessBlock.php

@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\KeyValueStore\KeyValueStoreInterface;
+use Drupal\Core\Plugin\ContainerFactoryPluginInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Symfony\Component\DependencyInjection\ContainerInterface;
+
+/**
+ * Provides a block to test access.
+ */
+#[Block(
+  id: "test_access",
+  admin_label: new TranslatableMarkup("Test block access"),
+)]
+class TestAccessBlock extends BlockBase implements ContainerFactoryPluginInterface {
+
+  /**
+   * Tests the test access block.
+   *
+   * @param array $configuration
+   *   The plugin configuration, i.e. an array with configuration values keyed
+   *   by configuration option name. The special key 'context' may be used to
+   *   initialize the defined contexts by setting it to an array of context
+   *   values keyed by context names.
+   * @param string $plugin_id
+   *   The plugin ID for the plugin instance.
+   * @param mixed $plugin_definition
+   *   The plugin implementation definition.
+   * @param \Drupal\Core\KeyValueStore\KeyValueStoreInterface $keyValue
+   *   The key value store.
+   */
+  public function __construct(array $configuration, $plugin_id, $plugin_definition, protected KeyValueStoreInterface $keyValue) {
+    parent::__construct($configuration, $plugin_id, $plugin_definition);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
+    return new static(
+      $configuration,
+      $plugin_id,
+      $plugin_definition,
+      $container->get('keyvalue')->get('block_test')
+    );
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account) {
+    return $this->keyValue->get('access', FALSE) ? AccessResult::allowed()->setCacheMaxAge(0) : AccessResult::forbidden()->setCacheMaxAge(0);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return ['#markup' => 'Hello test world'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return Cache::PERMANENT;
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestBlockInstantiation.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a basic block for testing block instantiation and configuration.
+ */
+#[Block(
+  id: "test_block_instantiation",
+  admin_label: new TranslatableMarkup("Display message")
+)]
+class TestBlockInstantiation extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function defaultConfiguration() {
+    return [
+      'display_message' => 'no message set',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account) {
+    return AccessResult::allowedIfHasPermission($account, 'access content');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    $form['display_message'] = [
+      '#type' => 'textfield',
+      '#title' => $this->t('Display message'),
+      '#default_value' => $this->configuration['display_message'],
+    ];
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockSubmit($form, FormStateInterface $form_state) {
+    $this->configuration['display_message'] = $form_state->getValue('display_message');
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#children' => $this->configuration['display_message'],
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestCacheBlock.php

@@ -0,0 +1,47 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block to test caching.
+ */
+#[Block(
+  id: "test_cache",
+  admin_label: new TranslatableMarkup("Test block caching")
+)]
+class TestCacheBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    $content = \Drupal::keyValue('block_test')->get('content');
+
+    $build = [];
+    if (!empty($content)) {
+      $build['#markup'] = $content;
+    }
+    return $build;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheContexts() {
+    return \Drupal::state()->get('block_test.cache_contexts', []);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getCacheMaxAge() {
+    return \Drupal::state()->get('block_test.cache_max_age', parent::getCacheMaxAge());
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestContextAwareBlock.php

@@ -0,0 +1,57 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\Context\EntityContextDefinition;
+use Drupal\Core\Session\AccountInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\user\UserInterface;
+
+/**
+ * Provides a context-aware block.
+ */
+#[Block(
+  id: "test_context_aware",
+  admin_label: new TranslatableMarkup("Test context-aware block"),
+  context_definitions: [
+    'user' => new EntityContextDefinition(
+      data_type: 'entity:user',
+      label: new TranslatableMarkup("User Context"),
+      required: FALSE,
+      constraints: [
+        "NotNull" => [],
+      ]
+    ),
+  ]
+)]
+class TestContextAwareBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    /** @var \Drupal\user\UserInterface $user */
+    $user = $this->getContextValue('user');
+    return [
+      '#prefix' => '<div id="' . $this->getPluginId() . '--username">',
+      '#suffix' => '</div>',
+      '#markup' => $user ? $user->getAccountName() : 'No context mapping selected.',
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function blockAccess(AccountInterface $account) {
+    if ($this->getContextValue('user') instanceof UserInterface) {
+      $this->messenger()->addStatus('User context found.');
+    }
+
+    return parent::blockAccess($account);
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestContextAwareNoValidContextOptionsBlock.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\Context\ContextDefinition;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a context-aware block that uses a not-passed, non-required context.
+ */
+#[Block(
+  id: "test_context_aware_no_valid_context_options",
+  admin_label: new TranslatableMarkup("Test context-aware block - no valid context options"),
+  context_definitions: [
+    'user' => new ContextDefinition(data_type: 'email', required: FALSE),
+  ]
+)]
+class TestContextAwareNoValidContextOptionsBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#markup' => 'Rendered block with no valid context options',
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestContextAwareUnsatisfiedBlock.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\Context\EntityContextDefinition;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a context-aware block.
+ */
+#[Block(
+  id: "test_context_aware_unsatisfied",
+  admin_label: new TranslatableMarkup("Test context-aware unsatisfied block"),
+  context_definitions: [
+    'user' => new EntityContextDefinition('entity:foobar'),
+  ]
+)]
+class TestContextAwareUnsatisfiedBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#markup' => 'test',
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestEmptyBlock.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block that returns an empty array.
+ */
+#[Block(
+  id: "test_empty",
+  admin_label: new TranslatableMarkup("Test Empty block"),
+)]
+class TestEmptyBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestFormBlock.php

@@ -0,0 +1,27 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block to test caching.
+ */
+#[Block(
+  id: "test_form_in_block",
+  admin_label: new TranslatableMarkup("Test form block caching"),
+)]
+class TestFormBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return \Drupal::formBuilder()->getForm('Drupal\block_test\Form\TestForm');
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestHtmlBlock.php

@@ -0,0 +1,30 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block to test HTML.
+ */
+#[Block(
+  id: "test_html",
+  admin_label: new TranslatableMarkup("Test HTML block"),
+)]
+class TestHtmlBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [
+      '#attributes' => \Drupal::keyvalue('block_test')->get('attributes'),
+      '#children' => \Drupal::keyValue('block_test')->get('content'),
+    ];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestMultipleFormsBlock.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\block_test\PluginForm\EmptyBlockForm;
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a block with multiple forms.
+ */
+#[Block(
+  id: "test_multiple_forms_block",
+  forms: [
+    'secondary' => EmptyBlockForm::class,
+  ],
+  admin_label: new TranslatableMarkup("Multiple forms test block"),
+)]
+class TestMultipleFormsBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return [];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Block/TestSettingsValidationBlock.php

@@ -0,0 +1,44 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Block;
+
+use Drupal\Core\Block\Attribute\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a test settings validation block.
+ */
+#[Block(
+  id: "test_settings_validation",
+  admin_label: new TranslatableMarkup("Test settings validation block"),
+)]
+class TestSettingsValidationBlock extends BlockBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockForm($form, FormStateInterface $form_state) {
+    return ['digits' => ['#type' => 'textfield']] + $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function blockValidate($form, FormStateInterface $form_state) {
+    if (!ctype_digit($form_state->getValue('digits'))) {
+      $form_state->setErrorByName('digits', $this->t('Only digits are allowed'));
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function build() {
+    return ['#markup' => 'foo'];
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Condition/BaloneySpam.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Condition;
+
+use Drupal\Core\Condition\Attribute\Condition;
+use Drupal\Core\Condition\ConditionPluginBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a 'baloney_spam' condition.
+ */
+#[Condition(
+  id: "baloney_spam",
+  label: new TranslatableMarkup("Baloney spam"),
+)]
+class BaloneySpam extends ConditionPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function evaluate() {
+    return TRUE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function summary() {
+    return 'Summary';
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/Plugin/Condition/MissingSchema.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\Plugin\Condition;
+
+use Drupal\Core\Condition\Attribute\Condition;
+use Drupal\Core\Condition\ConditionPluginBase;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+
+/**
+ * Provides a 'missing_schema' condition.
+ */
+#[Condition(
+  id: "missing_schema",
+  label: new TranslatableMarkup("Missing schema"),
+)]
+class MissingSchema extends ConditionPluginBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public function evaluate() {
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function summary() {
+    return 'Summary';
+  }
+
+}

web/core/modules/block/tests/modules/block_test/src/PluginForm/EmptyBlockForm.php

@@ -0,0 +1,34 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\block_test\PluginForm;
+
+use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginFormBase;
+
+/**
+ * Provides a form for a block that is empty.
+ */
+class EmptyBlockForm extends PluginFormBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  public $plugin;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function buildConfigurationForm(array $form, FormStateInterface $form_state) {
+    return $form;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function submitConfigurationForm(array &$form, FormStateInterface $form_state) {
+    // Intentionally empty.
+  }
+
+}

web/core/modules/block/tests/modules/block_test/themes/block_test_special_chars_theme/block_test_special_chars_theme.info.yml

@@ -0,0 +1,7 @@
+name: '<"Cat" & ''Mouse''>'
+type: theme
+base theme: stable9
+description: 'Theme for testing special characters in block admin.'
+regions:
+  content: Content
+  help: Help

web/core/modules/block/tests/modules/block_test/themes/block_test_theme/block_test_theme.info.yml

@@ -0,0 +1,16 @@
+name: 'Block test theme'
+type: theme
+base theme: stable9
+description: 'Theme for testing the block system'
+version: VERSION
+regions:
+  sidebar_first: 'Left sidebar'
+  sidebar_second: 'Right sidebar'
+  content: Content
+  header: Header
+  footer: Footer
+  highlighted: Highlighted
+  help: Help
+regions_hidden:
+  - sidebar_first
+  - sidebar_second

web/core/modules/block/tests/modules/block_test_views/block_test_views.info.yml

@@ -0,0 +1,8 @@
+name: 'Block test views'
+type: module
+description: 'Provides a view and block to test block displays in views.'
+package: Testing
+version: VERSION
+dependencies:
+  - drupal:block
+  - drupal:views

web/core/modules/block/tests/modules/block_test_views/test_views/views.view.test_view_block.yml

@@ -0,0 +1,56 @@
+langcode: en
+status: true
+dependencies: {  }
+id: test_view_block
+label: test_view_block
+module: views
+description: ''
+tag: ''
+base_table: views_test_data
+base_field: id
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: null
+    display_options:
+      access:
+        type: none
+      cache:
+        type: tag
+      query:
+        type: views_query
+      exposed_form:
+        type: basic
+      pager:
+        type: some
+        options:
+          items_per_page: 5
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        name:
+          id: name
+          table: views_test_data
+          field: name
+      title: test_view_block
+      footer:
+        area_text_custom:
+          id: area_text_custom
+          table: views
+          field: area_text_custom
+          relationship: none
+          group_type: group
+          admin_label: ''
+          plugin_id: text_custom
+          empty: false
+          content: '[view:title]'
+          tokenize: false
+  block_1:
+    display_plugin: block
+    id: block_1
+    display_title: Block
+    position: null

web/core/modules/block/tests/modules/block_test_views/test_views/views.view.test_view_block2.yml

@@ -0,0 +1,56 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - user
+id: test_view_block2
+label: test_view_block2
+module: views
+description: ''
+tag: ''
+base_table: views_test_data
+base_field: id
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: null
+    display_options:
+      access:
+        type: perm
+      cache:
+        type: tag
+      query:
+        type: views_query
+      exposed_form:
+        type: basic
+      pager:
+        type: some
+        options:
+          items_per_page: 5
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        name:
+          id: name
+          table: views_test_data
+          field: name
+      title: test_view_block2
+  block_1:
+    display_plugin: block
+    id: block_1
+    display_title: Block
+    position: null
+  block_2:
+    display_plugin: block
+    id: block_2
+    display_title: Block
+    position: null
+  block_3:
+    display_plugin: block
+    id: block_3
+    display_title: Block
+    position: null

web/core/modules/block/tests/modules/block_test_views/test_views/views.view.test_view_block_with_context.yml

@@ -0,0 +1,426 @@
+langcode: en
+status: true
+dependencies:
+  module:
+    - node
+    - user
+id: test_view_block_with_context
+label: test_view_block_with_context
+module: views
+description: ''
+tag: ''
+base_table: node_field_data
+base_field: nid
+display:
+  default:
+    display_plugin: default
+    id: default
+    display_title: Default
+    position: 0
+    display_options:
+      access:
+        type: perm
+        options:
+          perm: 'access content'
+      cache:
+        type: tag
+        options: {  }
+      query:
+        type: views_query
+        options:
+          disable_sql_rewrite: false
+          distinct: false
+          replica: false
+          query_comment: ''
+          query_tags: {  }
+      exposed_form:
+        type: basic
+        options:
+          submit_button: Apply
+          reset_button: false
+          reset_button_label: Reset
+          exposed_sorts_label: 'Sort by'
+          expose_sort_order: true
+          sort_asc_label: Asc
+          sort_desc_label: Desc
+      pager:
+        type: some
+        options:
+          items_per_page: 5
+          offset: 0
+      style:
+        type: default
+      row:
+        type: fields
+      fields:
+        title:
+          id: title
+          table: node_field_data
+          field: title
+          relationship: none
+          group_type: group
+          admin_label: ''
+          label: ''
+          exclude: false
+          alter:
+            alter_text: true
+            text: 'Test view row: {{ title }}'
+            make_link: false
+            path: ''
+            absolute: false
+            external: false
+            replace_spaces: false
+            path_case: none
+            trim_whitespace: false
+            alt: ''
+            rel: ''
+            link_class: ''
+            prefix: ''
+            suffix: ''
+            target: ''
+            nl2br: false
+            max_length: 0
+            word_boundary: true
+            ellipsis: true
+            more_link: false
+            more_link_text: ''
+            more_link_path: ''
+            strip_tags: false
+            trim: false
+            preserve_tags: ''
+            html: false
+          element_type: ''
+          element_class: ''
+          element_label_type: ''
+          element_label_class: ''
+          element_label_colon: false
+          element_wrapper_type: ''
+          element_wrapper_class: ''
+          element_default_classes: true
+          empty: ''
+          hide_empty: false
+          empty_zero: false
+          hide_alter_empty: true
+          click_sort_column: value
+          type: string
+          settings:
+            link_to_entity: true
+          group_column: value
+          group_columns: {  }
+          group_rows: true
+          delta_limit: 0
+          delta_offset: 0
+          delta_reversed: false
+          delta_first_last: false
+          multi_type: separator
+          separator: ', '
+          field_api_classes: false
+          plugin_id: field
+      filters:
+        status:
+          value: '1'
+          table: node_field_data
+          field: status
+          plugin_id: boolean
+          entity_type: node
+          entity_field: status
+          id: status
+          expose:
+            operator: ''
+          group: 1
+      sorts:
+        created:
+          id: created
+          table: node_field_data
+          field: created
+          order: DESC
+          entity_type: node
+          entity_field: created
+          plugin_id: date
+          relationship: none
+          group_type: group
+          admin_label: ''
+          exposed: false
+          expose:
+            label: ''
+          granularity: second
+      title: test_view_block_with_context
+      header: {  }
+      footer: {  }
+      empty:
+        area_text_custom:
+          id: area_text_custom
+          table: views
+          field: area_text_custom
+          relationship: none
+          group_type: group
+          admin_label: ''
+          empty: true
+          tokenize: false
+          content: 'Test view: No results found.'
+          plugin_id: text_custom
+      relationships: {  }
+      arguments:
+        'null':
+          id: 'null'
+          table: views
+          field: 'null'
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: default
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: foo
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          must_not_be: false
+          plugin_id: 'null'
+        null_1:
+          id: null_1
+          table: views
+          field: 'null'
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          must_not_be: false
+          plugin_id: 'null'
+        nid:
+          id: nid
+          table: node_field_data
+          field: nid
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: empty
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: true
+          validate:
+            type: 'entity:node'
+            fail: 'not found'
+          validate_options:
+            operation: view
+            multiple: 0
+            bundles: {  }
+            access: false
+          break_phrase: false
+          not: false
+          entity_type: node
+          entity_field: nid
+          plugin_id: node_nid
+      display_extenders: {  }
+    cache_metadata:
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - 'user.node_grants:view'
+        - user.permissions
+      cacheable: false
+      max-age: -1
+      tags: {  }
+  block_1:
+    display_plugin: block
+    id: block_1
+    display_title: Block
+    position: 1
+    display_options:
+      display_extenders: {  }
+    cache_metadata:
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - 'user.node_grants:view'
+        - user.permissions
+      cacheable: false
+      max-age: -1
+      tags: {  }
+  block_2:
+    display_plugin: block
+    id: block_2
+    display_title: 'Block 2'
+    position: 2
+    display_options:
+      display_extenders: {  }
+      arguments:
+        created:
+          id: created
+          table: node_field_data
+          field: created
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: true
+          validate:
+            type: numeric
+            fail: 'not found'
+          validate_options: {  }
+          entity_type: node
+          entity_field: created
+          plugin_id: date
+        vid:
+          id: vid
+          table: node_field_data
+          field: vid
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          break_phrase: false
+          not: false
+          entity_type: node
+          entity_field: vid
+          plugin_id: numeric
+        title:
+          id: title
+          table: node_field_data
+          field: title
+          relationship: none
+          group_type: group
+          admin_label: ''
+          default_action: ignore
+          exception:
+            value: all
+            title_enable: false
+            title: All
+          title_enable: false
+          title: ''
+          default_argument_type: fixed
+          default_argument_options:
+            argument: ''
+          summary_options:
+            base_path: ''
+            count: true
+            items_per_page: 25
+            override: false
+          summary:
+            sort_order: asc
+            number_of_records: 0
+            format: default_summary
+          specify_validation: false
+          validate:
+            type: none
+            fail: 'not found'
+          validate_options: {  }
+          glossary: false
+          limit: 0
+          case: none
+          path_case: none
+          transform_dash: false
+          break_phrase: false
+          entity_type: node
+          entity_field: title
+          plugin_id: string
+      defaults:
+        arguments: false
+    cache_metadata:
+      max-age: -1
+      contexts:
+        - 'languages:language_content'
+        - 'languages:language_interface'
+        - url
+        - 'user.node_grants:view'
+        - user.permissions
+      tags: {  }

web/core/modules/block/tests/src/Functional/AssertBlockAppearsTrait.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\block\Entity\Block;
+
+/**
+ * Provides test assertions for testing block appearance.
+ *
+ * Can be used by test classes that extend \Drupal\Tests\BrowserTestBase.
+ */
+trait AssertBlockAppearsTrait {
+
+  /**
+   * Checks to see whether a block appears on the page.
+   *
+   * @param \Drupal\block\Entity\Block $block
+   *   The block entity to find on the page.
+   */
+  protected function assertBlockAppears(Block $block) {
+    $this->assertSession()->elementExists('xpath', "//div[@id = 'block-{$block->id()}']");
+  }
+
+  /**
+   * Checks to see whether a block does not appears on the page.
+   *
+   * @param \Drupal\block\Entity\Block $block
+   *   The block entity to find on the page.
+   */
+  protected function assertNoBlockAppears(Block $block) {
+    $this->assertSession()->elementNotExists('xpath', "//div[@id = 'block-{$block->id()}']");
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockAdminThemeTest.php

@@ -0,0 +1,87 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the block system with admin themes.
+ *
+ * @group block
+ */
+class BlockAdminThemeTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'contextual'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Check for the accessibility of the admin theme on the block admin page.
+   */
+  public function testAdminTheme(): void {
+    // Create administrative user.
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Ensure that access to block admin page is denied when theme is not
+    // installed.
+    $this->drupalGet('admin/structure/block/list/olivero');
+    $this->assertSession()->statusCodeEquals(403);
+
+    // Install admin theme and confirm that tab is accessible.
+    \Drupal::service('theme_installer')->install(['olivero']);
+    $edit['admin_theme'] = 'olivero';
+    $this->drupalGet('admin/appearance');
+    $this->submitForm($edit, 'Save configuration');
+    $this->drupalGet('admin/structure/block/list/olivero');
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
+  /**
+   * Ensure contextual links are disabled in Claro theme.
+   */
+  public function testClaroAdminTheme(): void {
+    // Create administrative user.
+    $admin_user = $this->drupalCreateUser([
+      'access administration pages',
+      'administer themes',
+      'access contextual links',
+      'view the administration theme',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Install admin theme and confirm that tab is accessible.
+    \Drupal::service('theme_installer')->install(['claro']);
+    $edit['admin_theme'] = 'claro';
+    $this->drupalGet('admin/appearance');
+    $this->submitForm($edit, 'Save configuration');
+
+    // Define our block settings.
+    $settings = [
+      'theme' => 'claro',
+      'region' => 'header',
+    ];
+
+    // Place a block.
+    $block = $this->drupalPlaceBlock('local_tasks_block', $settings);
+
+    // Open admin page.
+    $this->drupalGet('admin');
+
+    // Check if contextual link classes are unavailable.
+    $this->assertSession()->responseNotContains('<div data-contextual-id="block:block=' . $block->id() . ':langcode=en"></div>');
+    $this->assertSession()->responseNotContains('contextual-region');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockCacheTest.php

@@ -0,0 +1,240 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Core\Cache\Cache;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests block caching.
+ *
+ * @group block
+ */
+class BlockCacheTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'test_page_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * A user with permission to administer blocks.
+   *
+   * @var object
+   */
+  protected $adminUser;
+
+  /**
+   * An authenticated user to test block caching.
+   *
+   * @var object
+   */
+  protected $normalUser;
+
+  /**
+   * Another authenticated user to test block caching.
+   *
+   * @var object
+   */
+  protected $normalUserAlt;
+
+  /**
+   * The block used by this test.
+   *
+   * @var \Drupal\block\BlockInterface
+   */
+  protected $block;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create an admin user, log in and enable test blocks.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]);
+    $this->drupalLogin($this->adminUser);
+
+    // Create additional users to test caching modes.
+    $this->normalUser = $this->drupalCreateUser();
+    $this->normalUserAlt = $this->drupalCreateUser();
+    // Sync the roles, since drupalCreateUser() creates separate roles for
+    // the same permission sets.
+    $this->normalUserAlt->roles = $this->normalUser->getRoles();
+    $this->normalUserAlt->save();
+
+    // Enable our test block.
+    $this->block = $this->drupalPlaceBlock('test_cache');
+  }
+
+  /**
+   * Tests "user.roles" cache context.
+   */
+  public function testCachePerRole(): void {
+    \Drupal::state()->set('block_test.cache_contexts', ['user.roles']);
+
+    // Enable our test block. Set some content for it to display.
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalLogin($this->normalUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    // Change the content, but the cached copy should still be served.
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Clear the cache and verify that the stale data is no longer there.
+    Cache::invalidateTags(['block_view']);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($old_content);
+    // Fresh block content is displayed after clearing the cache.
+    $this->assertSession()->pageTextContains($current_content);
+
+    // Test whether the cached data is served for the correct users.
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalLogout();
+    $this->drupalGet('');
+    // Anonymous user does not see content cached per-role for normal user.
+    $this->assertSession()->pageTextNotContains($old_content);
+
+    // User with the same roles sees per-role cached content.
+    $this->drupalLogin($this->normalUserAlt);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Admin user does not see content cached per-role for normal user.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($old_content);
+
+    // Block is served from the per-role cache.
+    $this->drupalLogin($this->normalUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+  }
+
+  /**
+   * Tests a cacheable block without any additional cache context.
+   */
+  public function testCachePermissions(): void {
+    // user.permissions is a required context, so a user with different
+    // permissions will see a different version of the block.
+    \Drupal::state()->set('block_test.cache_contexts', []);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    // Block content served from cache.
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Block content not served from cache.
+    $this->drupalLogout();
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextContains($current_content);
+  }
+
+  /**
+   * Tests non-cacheable block.
+   */
+  public function testNoCache(): void {
+    \Drupal::state()->set('block_test.cache_max_age', 0);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    // If max_age = 0 has no effect, the next request would be cached.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    // A cached copy should not be served.
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalGet('');
+    // Maximum age of zero prevents blocks from being cached.
+    $this->assertSession()->pageTextContains($current_content);
+  }
+
+  /**
+   * Tests "user" cache context.
+   */
+  public function testCachePerUser(): void {
+    \Drupal::state()->set('block_test.cache_contexts', ['user']);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+    $this->drupalLogin($this->normalUser);
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    // Block is served from per-user cache.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+
+    // Per-user block cache is not served for other users.
+    $this->drupalLogin($this->normalUserAlt);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($current_content);
+
+    // Per-user block cache is persistent.
+    $this->drupalLogin($this->normalUser);
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($old_content);
+  }
+
+  /**
+   * Tests "url" cache context.
+   */
+  public function testCachePerPage(): void {
+    \Drupal::state()->set('block_test.cache_contexts', ['url']);
+
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    $this->drupalGet('test-page');
+    $this->assertSession()->pageTextContains($current_content);
+
+    $old_content = $current_content;
+    $current_content = $this->randomMachineName();
+    \Drupal::keyValue('block_test')->set('content', $current_content);
+
+    $this->drupalGet('user');
+    $this->assertSession()->statusCodeEquals(200);
+    // Verify that block content cached for the test page does not show up
+    // for the user page.
+    $this->assertSession()->pageTextNotContains($old_content);
+    $this->drupalGet('test-page');
+    $this->assertSession()->statusCodeEquals(200);
+    // Verify that the block content is cached for the test page.
+    $this->assertSession()->pageTextContains($old_content);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockDemoTest.php

@@ -0,0 +1,70 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the block demo page with admin themes.
+ *
+ * @group block
+ */
+class BlockDemoTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Check for the accessibility of the admin block demo page.
+   */
+  public function testBlockDemo(): void {
+    // Create administrative user.
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Confirm we have access to the block demo page for the default theme.
+    $config = $this->container->get('config.factory')->get('system.theme');
+    $default_theme = $config->get('default');
+    $this->drupalGet('admin/structure/block/demo/' . $default_theme);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->linkByHrefExists('admin/structure/block');
+    $this->assertSession()->linkByHrefNotExists('admin/structure/block/list/' . $default_theme);
+
+    // All available themes in core.
+    $available_themes = [
+      'olivero',
+      'claro',
+      'stark',
+    ];
+
+    // All available themes minute minus the default theme.
+    $themes = array_diff($available_themes, [$default_theme]);
+
+    foreach ($themes as $theme) {
+      // Install theme.
+      $this->container->get('theme_installer')->install([$theme]);
+      // Confirm access to the block demo page for the theme.
+      $this->drupalGet('admin/structure/block/demo/' . $theme);
+      $this->assertSession()->statusCodeEquals(200);
+      // Confirm existence of link for "Exit block region demonstration".
+      $this->assertSession()->linkByHrefExists('admin/structure/block/list/' . $theme);
+    }
+
+    // Confirm access to the block demo page is denied for an invalid theme.
+    $this->drupalGet('admin/structure/block/demo/invalid_theme');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockFormInBlockTest.php

@@ -0,0 +1,77 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Component\Utility\Crypt;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests form in block caching.
+ *
+ * @group block
+ */
+class BlockFormInBlockTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'test_page_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Enable our test block.
+    $this->drupalPlaceBlock('test_form_in_block');
+  }
+
+  /**
+   * Tests to see if form in block's redirect isn't cached.
+   */
+  public function testCachePerPage(): void {
+    $form_values = ['email' => 'test@example.com'];
+
+    // Go to "test-page" and test if the block is enabled.
+    $this->drupalGet('test-page');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Your .com email address.');
+
+    // Make sure that we're currently still on /test-page after submitting the
+    // form.
+    $this->submitForm($form_values, 'Submit');
+    $this->assertSession()->addressEquals('test-page');
+    $this->assertSession()->pageTextContains('Your email address is test@example.com');
+
+    // Go to a different page and see if the block is enabled there as well.
+    $this->drupalGet('test-render-title');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Your .com email address.');
+
+    // Make sure that submitting the form didn't redirect us to the first page
+    // we submitted the form from after submitting the form from
+    // /test-render-title.
+    $this->submitForm($form_values, 'Submit');
+    $this->assertSession()->addressEquals('test-render-title');
+    $this->assertSession()->pageTextContains('Your email address is test@example.com');
+  }
+
+  /**
+   * Tests the actual placeholders.
+   */
+  public function testPlaceholders(): void {
+    $this->drupalGet('test-multiple-forms');
+
+    $placeholder = 'form_action_' . Crypt::hashBase64('Drupal\Core\Form\FormBuilder::prepareForm');
+    $this->assertSession()->pageTextContains('Form action: ' . $placeholder);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockHiddenRegionTest.php

@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests that blocks are not added to hidden regions on theme installation.
+ *
+ * @group block
+ */
+class BlockHiddenRegionTest extends BrowserTestBase {
+
+  /**
+   * An administrative user to configure the test environment.
+   *
+   * @var \Drupal\user\Entity\User|false
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'search'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create administrative user.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+      'search content',
+    ]);
+
+    $this->drupalLogin($this->adminUser);
+    $this->drupalPlaceBlock('search_form_block');
+    $this->drupalPlaceBlock('local_tasks_block');
+  }
+
+  /**
+   * Tests that hidden regions do not inherit blocks when a theme is installed.
+   */
+  public function testBlockNotInHiddenRegion(): void {
+
+    // Ensure that the search form block is displayed.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('Search');
+
+    // Install "block_test_theme" and set it as the default theme.
+    $theme = 'block_test_theme';
+    // We need to install a non-hidden theme so that there is more than one
+    // local task.
+    \Drupal::service('theme_installer')->install([$theme, 'stark']);
+    $this->config('system.theme')
+      ->set('default', $theme)
+      ->save();
+    // Installing a theme will cause the kernel terminate event to rebuild the
+    // router. Simulate that here.
+    \Drupal::service('router.builder')->rebuildIfNeeded();
+
+    // Ensure that "block_test_theme" is set as the default theme.
+    $this->drupalGet('admin/structure/block');
+    $this->assertSession()->pageTextContains('Block test theme');
+
+    // Ensure that the search form block is displayed.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('Search');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockHookOperationTest.php

@@ -0,0 +1,58 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests for Block module regarding hook_entity_operations_alter().
+ *
+ * @group block
+ */
+class BlockHookOperationTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'entity_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $permissions = [
+      'administer blocks',
+    ];
+
+    // Create and log in user.
+    $admin_user = $this->drupalCreateUser($permissions);
+    $this->drupalLogin($admin_user);
+  }
+
+  /**
+   * Tests the block list to see if the test_operation link is added.
+   */
+  public function testBlockOperationAlter(): void {
+    // Add a test block, any block will do.
+    // Set the machine name so the test_operation link can be built later.
+    $block_id = $this->randomMachineName(16);
+    $this->drupalPlaceBlock('system_powered_by_block', ['id' => $block_id]);
+
+    // Get the Block listing.
+    $this->drupalGet('admin/structure/block');
+
+    $test_operation_link = 'admin/structure/block/manage/' . $block_id . '/test_operation';
+    // Test if the test_operation link is on the page.
+    $this->assertSession()->linkByHrefExists($test_operation_link);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockHtmlTest.php

@@ -0,0 +1,60 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests block HTML ID validity.
+ *
+ * @group block
+ */
+class BlockHtmlTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]));
+
+    // Enable the test_html block, to test HTML ID and attributes.
+    \Drupal::keyValue('block_test')->set('attributes', ['data-custom-attribute' => 'foo']);
+    \Drupal::keyValue('block_test')->set('content', $this->randomMachineName());
+    $this->drupalPlaceBlock('test_html', ['id' => 'test_html_block']);
+
+    // Enable a menu block, to test more complicated HTML.
+    $this->drupalPlaceBlock('system_menu_block:admin', ['id' => 'test_menu_block']);
+  }
+
+  /**
+   * Tests for valid HTML for a block.
+   */
+  public function testHtml(): void {
+    $this->drupalGet('');
+
+    // Ensure that a block's ID is converted to an HTML valid ID, and that
+    // block-specific attributes are added to the same DOM element.
+    $this->assertSession()->elementExists('xpath', '//div[@id="block-test-html-block" and @data-custom-attribute="foo"]');
+
+    // Ensure expected markup for a menu block.
+    $this->assertSession()->elementExists('xpath', '//nav[@id="block-test-menu-block"]/ul/li');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockInstallTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests block module's installation.
+ *
+ * @group block
+ */
+class BlockInstallTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests cache tag invalidation after installing the block module.
+   */
+  public function testCacheTagInvalidationUponInstallation(): void {
+    // Warm the page cache.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->assertSession()->responseHeaderNotContains('X-Drupal-Cache-Tags', 'config:block_list');
+
+    // Install the block module, and place the "Powered by Drupal" block.
+    $this->container->get('module_installer')->install(['block', 'shortcut']);
+    $this->rebuildContainer();
+    $this->drupalPlaceBlock('system_powered_by_block');
+
+    // Check the same page, block.module's hook_install() should have
+    // invalidated the 'rendered' cache tag to make blocks show up.
+    $this->drupalGet('');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:block_list');
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockInvalidRegionTest.php

@@ -0,0 +1,83 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests that blocks assigned to invalid regions are disabled with a warning.
+ *
+ * @group block
+ */
+class BlockInvalidRegionTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $configSchemaCheckerExclusions = [
+    // This block is intentionally put in an invalid region, so it will violate
+    // config schema.
+    // @see ::testBlockInvalidRegion()
+    'block.block.invalid_region',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Create an admin user.
+    $admin_user = $this->drupalCreateUser([
+      'administer site configuration',
+      'access administration pages',
+      'administer blocks',
+    ]);
+    $this->drupalLogin($admin_user);
+  }
+
+  /**
+   * Tests that blocks assigned to invalid regions work correctly.
+   */
+  public function testBlockInInvalidRegion(): void {
+    // Enable a test block and place it in an invalid region.
+    $block = $this->drupalPlaceBlock('test_html', ['id' => 'invalid_region']);
+    \Drupal::configFactory()->getEditable('block.block.' . $block->id())->set('region', 'invalid_region')->save();
+    $block = Block::load($block->id());
+
+    $warning_message = 'The block ' . $block->id() . ' was assigned to the invalid region invalid_region and has been disabled.';
+
+    // Clearing the cache should disable the test block placed in the invalid
+    // region.
+    $this->drupalGet('admin/config/development/performance');
+    $this->submitForm([], 'Clear all caches');
+    $this->assertSession()->statusMessageContains($warning_message, 'warning');
+
+    // Clear the cache to check if the warning message is not triggered.
+    $this->drupalGet('admin/config/development/performance');
+    $this->submitForm([], 'Clear all caches');
+    $this->assertSession()->statusMessageNotContains($warning_message, 'warning');
+
+    // Place disabled test block in the invalid region of the default theme.
+    \Drupal::configFactory()->getEditable('block.block.' . $block->id())->set('region', 'invalid_region')->save();
+    $block = Block::load($block->id());
+
+    // Clear the cache to check if the warning message is not triggered.
+    $this->drupalGet('admin/config/development/performance');
+    $this->submitForm([], 'Clear all caches');
+    $this->assertSession()->statusMessageNotContains($warning_message, 'warning');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockLanguageCacheTest.php

@@ -0,0 +1,85 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests display of menu blocks with multiple languages.
+ *
+ * @group block
+ */
+class BlockLanguageCacheTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'language', 'menu_ui'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * List of langcodes.
+   *
+   * @var array
+   */
+  protected $langcodes = [];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Create test languages.
+    $this->langcodes = [ConfigurableLanguage::load('en')];
+    for ($i = 1; $i < 3; ++$i) {
+      $language = ConfigurableLanguage::create([
+        'id' => 'l' . $i,
+        'label' => $this->randomString(),
+      ]);
+      $language->save();
+      $this->langcodes[$i] = $language;
+    }
+  }
+
+  /**
+   * Creates a block in a language, check blocks page in all languages.
+   */
+  public function testBlockLinks(): void {
+    // Create admin user to be able to access block admin.
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+      'administer menu',
+    ]);
+    $this->drupalLogin($admin_user);
+
+    // Create the block cache for all languages.
+    foreach ($this->langcodes as $langcode) {
+      $this->drupalGet('admin/structure/block', ['language' => $langcode]);
+      $this->clickLink('Place block');
+    }
+
+    // Create a menu in the default language.
+    $edit['label'] = $this->randomMachineName();
+    $edit['id'] = mb_strtolower($edit['label']);
+    $this->drupalGet('admin/structure/menu/add');
+    $this->submitForm($edit, 'Save');
+    $this->assertSession()->pageTextContains('Menu ' . $edit['label'] . ' has been added.');
+
+    // Check that the block is listed for all languages.
+    foreach ($this->langcodes as $langcode) {
+      $this->drupalGet('admin/structure/block', ['language' => $langcode]);
+      $this->clickLink('Place block');
+      $this->assertSession()->pageTextContains($edit['label']);
+    }
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockLanguageTest.php

@@ -0,0 +1,224 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests per-language block configuration.
+ *
+ * @group block
+ */
+class BlockLanguageTest extends BrowserTestBase {
+
+  /**
+   * An administrative user to configure the test environment.
+   *
+   * @var \Drupal\user\Entity\User|false
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['language', 'block', 'content_translation', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'administer languages',
+    ]);
+    $this->drupalLogin($this->adminUser);
+
+    // Add predefined language.
+    $edit = [
+      'predefined_langcode' => 'fr',
+    ];
+    $this->drupalGet('admin/config/regional/language/add');
+    $this->submitForm($edit, 'Add language');
+
+    // Verify that language was added successfully.
+    $this->assertSession()->pageTextContains('French');
+
+    // Set path prefixes for both languages.
+    $this->config('language.negotiation')->set('url', [
+      'source' => 'path_prefix',
+      'prefixes' => [
+        'en' => 'en',
+        'fr' => 'fr',
+      ],
+    ])->save();
+
+    $this->drupalCreateContentType(['type' => 'page']);
+    $this->drupalCreateNode();
+  }
+
+  /**
+   * Tests the visibility settings for the blocks based on language.
+   */
+  public function testLanguageBlockVisibility(): void {
+    // Check if the visibility setting is available.
+    $default_theme = $this->config('system.theme')->get('default');
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    // Ensure that the language visibility field is visible without a type
+    // setting.
+    $this->assertSession()->fieldExists('visibility[language][langcodes][en]');
+    $this->assertSession()->fieldNotExists('visibility[language][context_mapping][language]');
+
+    // Enable a standard block and set the visibility setting for one language.
+    $edit = [
+      'visibility[language][langcodes][en]' => TRUE,
+      'id' => $this->randomMachineName(8),
+      'region' => 'sidebar_first',
+    ];
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    // Change the default language.
+    $edit = [
+      'site_default_language' => 'fr',
+    ];
+    $this->drupalGet('admin/config/regional/language');
+    $this->submitForm($edit, 'Save configuration');
+
+    // Check that a page has a block.
+    $this->drupalGet('en');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+
+    // Check that a page doesn't has a block for the current language anymore.
+    $this->drupalGet('fr');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+  }
+
+  /**
+   * Tests if the visibility settings are removed if the language is deleted.
+   */
+  public function testLanguageBlockVisibilityLanguageDelete(): void {
+    // Enable a standard block and set the visibility setting for one language.
+    $edit = [
+      'visibility' => [
+        'language' => [
+          'langcodes' => [
+            'fr' => 'fr',
+          ],
+          'context_mapping' => ['language' => '@language.current_language_context:language_interface'],
+        ],
+      ],
+    ];
+    $block = $this->drupalPlaceBlock('system_powered_by_block', $edit);
+
+    // Check that we have the language in config after saving the setting.
+    $visibility = $block->getVisibility();
+    $this->assertEquals('fr', $visibility['language']['langcodes']['fr'], 'Language is set in the block configuration.');
+
+    // Delete the language.
+    $this->drupalGet('admin/config/regional/language/delete/fr');
+    $this->submitForm([], 'Delete');
+
+    // Check that the language is no longer stored in the configuration after
+    // it is deleted.
+    $block = Block::load($block->id());
+    $visibility = $block->getVisibility();
+    $this->assertArrayNotHasKey('language', $visibility, 'Language is no longer not set in the block configuration after deleting the block.');
+
+    // Ensure that the block visibility for language is gone from the UI.
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Configure');
+    $this->assertSession()->elementNotExists('xpath', '//details[@id="edit-visibility-language"]');
+  }
+
+  /**
+   * Tests block language visibility with different language types.
+   */
+  public function testMultipleLanguageTypes(): void {
+    // Customize content language detection to be different from interface
+    // language detection.
+    $edit = [
+      // Interface language detection: only using session.
+      'language_interface[enabled][language-url]' => FALSE,
+      'language_interface[enabled][language-session]' => TRUE,
+      // Content language detection: only using URL.
+      'language_content[configurable]' => TRUE,
+      'language_content[enabled][language-url]' => TRUE,
+      'language_content[enabled][language-interface]' => FALSE,
+    ];
+    $this->drupalGet('admin/config/regional/language/detection');
+    $this->submitForm($edit, 'Save settings');
+
+    // Check if the visibility setting is available with a type setting.
+    $default_theme = $this->config('system.theme')->get('default');
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    $this->assertSession()->fieldExists('visibility[language][langcodes][en]');
+    $this->assertSession()->fieldExists('visibility[language][context_mapping][language]');
+
+    // Enable a standard block and set visibility to French only.
+    $block_id = $this->randomMachineName(8);
+    $edit = [
+      'visibility[language][context_mapping][language]' => '@language.current_language_context:language_interface',
+      'visibility[language][langcodes][fr]' => TRUE,
+      'id' => $block_id,
+      'region' => 'sidebar_first',
+    ];
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    // Interface negotiation depends on request arguments.
+    $this->drupalGet('node/1', ['query' => ['language' => 'en']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('node/1', ['query' => ['language' => 'fr']]);
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+
+    // Log in again in order to clear the interface language stored in the
+    // session.
+    $this->drupalLogout();
+    $this->drupalLogin($this->adminUser);
+
+    // Content language does not depend on session/request arguments.
+    // It will fall back on English (site default) and not display the block.
+    $this->drupalGet('en');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('fr');
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+
+    // Change visibility to now depend on content language for this block.
+    $edit = [
+      'visibility[language][context_mapping][language]' => '@language.current_language_context:language_content',
+    ];
+    $this->drupalGet('admin/structure/block/manage/' . $block_id);
+    $this->submitForm($edit, 'Save block');
+
+    // Content language negotiation does not depend on request arguments.
+    // It will fall back on English (site default) and not display the block.
+    $this->drupalGet('node/1', ['query' => ['language' => 'en']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('node/1', ['query' => ['language' => 'fr']]);
+    $this->assertSession()->statusCodeEquals(200);
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+
+    // Content language negotiation depends on path prefix.
+    $this->drupalGet('en');
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->drupalGet('fr');
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockRenderOrderTest.php

@@ -0,0 +1,92 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests blocks are being rendered in order by weight.
+ *
+ * @group block
+ */
+class BlockRenderOrderTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['node', 'block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Create a test user.
+    $end_user = $this->drupalCreateUser([
+      'access content',
+    ]);
+    $this->drupalLogin($end_user);
+  }
+
+  /**
+   * Tests the render order of the blocks.
+   */
+  public function testBlockRenderOrder(): void {
+    // Enable test blocks and place them in the same region.
+    $region = 'header';
+    $test_blocks = [
+      'stark_powered' => [
+        'weight' => -3,
+        'id' => 'stark_powered',
+        'label' => 'Test block A',
+      ],
+      'stark_by' => [
+        'weight' => 3,
+        'id' => 'stark_by',
+        'label' => 'Test block C',
+      ],
+      'stark_drupal' => [
+        'weight' => 3,
+        'id' => 'stark_drupal',
+        'label' => 'Test block B',
+      ],
+    ];
+
+    // Place the test blocks.
+    foreach ($test_blocks as $test_block) {
+      $this->drupalPlaceBlock('system_powered_by_block', [
+        'label' => $test_block['label'],
+        'region' => $region,
+        'weight' => $test_block['weight'],
+        'id' => $test_block['id'],
+      ]);
+    }
+
+    $this->drupalGet('');
+    $test_content = $this->getSession()->getPage()->getContent();
+
+    $controller = $this->container->get('entity_type.manager')->getStorage('block');
+    foreach ($controller->loadMultiple() as $return_block) {
+      $id = $return_block->id();
+      if ($return_block_weight = $return_block->getWeight()) {
+        $this->assertSame((int) $test_blocks[$id]['weight'], $return_block_weight, 'Block weight is set as "' . $return_block_weight . '" for ' . $id . ' block.');
+        $position[$id] = strpos($test_content, Html::getClass('block-' . $test_blocks[$id]['id']));
+      }
+    }
+    // Verify that blocks with different weight are rendered in the correct
+    // order.
+    $this->assertLessThan($position['stark_by'], $position['stark_powered']);
+    // Verify that blocks with identical weight are rendered in alphabetical
+    // order.
+    $this->assertLessThan($position['stark_by'], $position['stark_drupal']);
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockSystemBrandingTest.php

@@ -0,0 +1,120 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+/**
+ * Tests branding block display.
+ *
+ * @group block
+ */
+class BlockSystemBrandingTest extends BlockTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'system'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Set a site slogan.
+    $this->config('system.site')
+      ->set('slogan', 'Community plumbing')
+      ->save();
+    // Add the system branding block to the page.
+    $this->drupalPlaceBlock('system_branding_block', ['region' => 'header', 'id' => 'site_branding']);
+  }
+
+  /**
+   * Tests system branding block configuration.
+   */
+  public function testSystemBrandingSettings(): void {
+    $site_logo_xpath = '//div[@id="block-site-branding"]/a/img';
+    $site_name_xpath = '//div[@id="block-site-branding"]/a[text() = "Drupal"]';
+    $site_slogan_xpath = '//div[@id="block-site-branding"]/descendant::text()[last()]';
+
+    // Set default block settings.
+    $this->drupalGet('');
+
+    // Test that all branding elements are displayed.
+    $this->assertSession()->elementExists('xpath', $site_logo_xpath);
+    $this->assertSession()->elementExists('xpath', $site_name_xpath);
+    $this->assertSession()->elementExists('xpath', $site_slogan_xpath);
+    $this->assertSession()->elementTextContains('xpath', $site_slogan_xpath, 'Community plumbing');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:system.site');
+    // Just this once, assert that the img src of the logo is as expected.
+    $theme_path = \Drupal::service('extension.list.theme')->getPath($this->defaultTheme);
+    $this->assertSession()->elementAttributeContains('xpath', $site_logo_xpath, 'src', $theme_path . '/logo.svg');
+
+    // Be sure the slogan is XSS-filtered.
+    $this->config('system.site')
+      ->set('slogan', '<script>alert("Community carpentry");</script>')
+      ->save();
+    $this->drupalGet('');
+    $this->assertSession()->elementTextEquals('xpath', $site_slogan_xpath, 'alert("Community carpentry");');
+    $this->assertSession()->responseNotContains('<script>alert("Community carpentry");</script>');
+
+    // Turn just the logo off.
+    $this->config('block.block.site_branding')
+      ->set('settings.use_site_logo', 0)
+      ->save();
+    $this->drupalGet('');
+
+    // Re-test all branding elements.
+    $this->assertSession()->elementNotExists('xpath', $site_logo_xpath);
+    $this->assertSession()->elementExists('xpath', $site_name_xpath);
+    $this->assertSession()->elementTextContains('xpath', $site_slogan_xpath, 'alert("Community carpentry");');
+    $this->assertSession()->responseNotContains('<script>alert("Community carpentry");</script>');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:system.site');
+
+    // Turn just the site name off.
+    $this->config('block.block.site_branding')
+      ->set('settings.use_site_logo', 1)
+      ->set('settings.use_site_name', 0)
+      ->save();
+    $this->drupalGet('');
+
+    // Re-test all branding elements.
+    $this->assertSession()->elementExists('xpath', $site_logo_xpath);
+    $this->assertSession()->elementNotExists('xpath', $site_name_xpath);
+    $this->assertSession()->elementTextContains('xpath', $site_slogan_xpath, 'alert("Community carpentry");');
+    $this->assertSession()->responseNotContains('<script>alert("Community carpentry");</script>');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:system.site');
+
+    // Turn just the site slogan off.
+    $this->config('block.block.site_branding')
+      ->set('settings.use_site_name', 1)
+      ->set('settings.use_site_slogan', 0)
+      ->save();
+    $this->drupalGet('');
+
+    // Re-test all branding elements.
+    $this->assertSession()->elementExists('xpath', $site_logo_xpath);
+    $this->assertSession()->elementExists('xpath', $site_name_xpath);
+    $this->assertSession()->elementTextNotContains('xpath', $site_slogan_xpath, 'Community carpentry');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:system.site');
+
+    // Turn the site name and the site slogan off.
+    $this->config('block.block.site_branding')
+      ->set('settings.use_site_name', 0)
+      ->set('settings.use_site_slogan', 0)
+      ->save();
+    $this->drupalGet('');
+
+    // Re-test all branding elements.
+    $this->assertSession()->elementExists('xpath', $site_logo_xpath);
+    $this->assertSession()->elementNotExists('xpath', $site_name_xpath);
+    $this->assertSession()->elementTextNotContains('xpath', $site_slogan_xpath, 'Community carpentry');
+    $this->assertSession()->responseHeaderContains('X-Drupal-Cache-Tags', 'config:system.site');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockTest.php

@@ -0,0 +1,646 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Component\Utility\Html;
+use Drupal\block\Entity\Block;
+use Drupal\Core\Url;
+use Drupal\user\Entity\Role;
+use Drupal\user\RoleInterface;
+
+/**
+ * Tests basic block functionality.
+ *
+ * @group block
+ */
+class BlockTest extends BlockTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests block visibility.
+   */
+  public function testBlockVisibility(): void {
+    $block_name = 'system_powered_by_block';
+    // Create a random title for the block.
+    $title = $this->randomMachineName(8);
+    // Enable a standard block.
+    $default_theme = $this->config('system.theme')->get('default');
+    $edit = [
+      'id' => $this->randomMachineName(8),
+      'region' => 'sidebar_first',
+      'settings[label]' => $title,
+      'settings[label_display]' => TRUE,
+    ];
+    // Set the block to be hidden on any user path, to be shown only to
+    // authenticated users, and to be shown only on 200 and 404 responses.
+    $edit['visibility[request_path][pages]'] = '/user*';
+    $edit['visibility[request_path][negate]'] = TRUE;
+    $edit['visibility[user_role][roles][' . RoleInterface::AUTHENTICATED_ID . ']'] = TRUE;
+    $edit['visibility[response_status][status_codes][200]'] = 200;
+    $edit['visibility[response_status][status_codes][404]'] = 404;
+    $this->drupalGet('admin/structure/block/add/' . $block_name . '/' . $default_theme);
+    $this->assertSession()->checkboxChecked('edit-visibility-request-path-negate-0');
+
+    $this->submitForm($edit, 'Save block');
+    $this->assertSession()->statusMessageContains('The block configuration has been saved.', 'status');
+
+    $this->clickLink('Configure');
+    $this->assertSession()->checkboxChecked('edit-visibility-request-path-negate-1');
+    $this->assertSession()->checkboxChecked('edit-visibility-response-status-status-codes-200');
+    $this->assertSession()->checkboxChecked('edit-visibility-response-status-status-codes-404');
+
+    // Confirm that the block is displayed on the front page (200 response).
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($title);
+
+    // Confirm that the block is not displayed according to path visibility
+    // rules.
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextNotContains($title);
+
+    // Confirm that the block is displayed on a 404 response.
+    $this->drupalGet('/0/null');
+    $this->assertSession()->pageTextContains($title);
+
+    // Confirm that the block is not displayed on a 403 response.
+    $this->drupalGet('/admin/config/system/cron');
+    $this->assertSession()->pageTextNotContains($title);
+
+    // Confirm that the block is not displayed to anonymous users.
+    $this->drupalLogout();
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($title);
+
+    // Confirm that an empty block is not displayed.
+    $this->assertSession()->pageTextNotContains('Powered by Drupal');
+    $this->assertSession()->responseNotContains('sidebar-first');
+  }
+
+  /**
+   * Tests that visibility can be properly toggled.
+   */
+  public function testBlockToggleVisibility(): void {
+    $block_name = 'system_powered_by_block';
+    // Create a random title for the block.
+    $title = $this->randomMachineName(8);
+    // Enable a standard block.
+    $default_theme = $this->config('system.theme')->get('default');
+    $edit = [
+      'id' => $this->randomMachineName(8),
+      'region' => 'sidebar_first',
+      'settings[label]' => $title,
+    ];
+    $block_id = $edit['id'];
+    // Set the block to be shown only to authenticated users.
+    $edit['visibility[user_role][roles][' . RoleInterface::AUTHENTICATED_ID . ']'] = TRUE;
+    $this->drupalGet('admin/structure/block/add/' . $block_name . '/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+    $this->clickLink('Configure');
+    $this->assertSession()->checkboxChecked('edit-visibility-user-role-roles-authenticated');
+
+    $edit = [
+      'visibility[user_role][roles][' . RoleInterface::AUTHENTICATED_ID . ']' => FALSE,
+    ];
+    $this->submitForm($edit, 'Save block');
+    $this->clickLink('Configure');
+    $this->assertSession()->checkboxNotChecked('edit-visibility-user-role-roles-authenticated');
+
+    // Ensure that no visibility is configured.
+    /** @var \Drupal\block\BlockInterface $block */
+    $block = Block::load($block_id);
+    $visibility_config = $block->getVisibilityConditions()->getConfiguration();
+    $this->assertSame([], $visibility_config);
+    $this->assertSame([], $block->get('visibility'));
+  }
+
+  /**
+   * Tests block visibility when leaving "pages" textarea empty.
+   */
+  public function testBlockVisibilityListedEmpty(): void {
+    $block_name = 'system_powered_by_block';
+    // Create a random title for the block.
+    $title = $this->randomMachineName(8);
+    // Enable a standard block.
+    $default_theme = $this->config('system.theme')->get('default');
+    $edit = [
+      'id' => $this->randomMachineName(8),
+      'region' => 'sidebar_first',
+      'settings[label]' => $title,
+      'visibility[request_path][negate]' => TRUE,
+    ];
+    // Set the block to be hidden on any user path, and to be shown only to
+    // authenticated users.
+    $this->drupalGet('admin/structure/block/add/' . $block_name . '/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+    $this->assertSession()->statusMessageContains('The block configuration has been saved.', 'status');
+
+    // Confirm that block was not displayed according to block visibility
+    // rules.
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextNotContains($title);
+
+    // Confirm that block was not displayed according to block visibility
+    // rules regardless of path case.
+    $this->drupalGet('USER');
+    $this->assertSession()->pageTextNotContains($title);
+
+    // Confirm that the block is not displayed to anonymous users.
+    $this->drupalLogout();
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains($title);
+  }
+
+  /**
+   * Tests adding a block from the library page with a weight query string.
+   */
+  public function testAddBlockFromLibraryWithWeight(): void {
+    $default_theme = $this->config('system.theme')->get('default');
+    // Test one positive, zero, and one negative weight.
+    foreach (['7', '0', '-9'] as $weight) {
+      $options = [
+        'query' => [
+          'region' => 'sidebar_first',
+          'weight' => $weight,
+        ],
+      ];
+      $this->drupalGet(Url::fromRoute('block.admin_library', ['theme' => $default_theme], $options));
+
+      $block_name = 'system_powered_by_block';
+      $add_url = Url::fromRoute('block.admin_add', [
+        'plugin_id' => $block_name,
+        'theme' => $default_theme,
+      ]);
+
+      // Verify that one link is found, with the expected link text.
+      $xpath = $this->assertSession()->buildXPathQuery('//a[contains(@href, :href)]', [':href' => $add_url->toString()]);
+      $this->assertSession()->elementsCount('xpath', $xpath, 1);
+      $this->assertSession()->elementTextEquals('xpath', $xpath, 'Place block');
+
+      $link = $this->getSession()->getPage()->find('xpath', $xpath);
+      [, $query_string] = explode('?', $link->getAttribute('href'), 2);
+      parse_str($query_string, $query_parts);
+      $this->assertEquals($weight, $query_parts['weight'], 'Found the expected weight query string.');
+
+      // Create a random title for the block.
+      $title = $this->randomMachineName(8);
+      $block_id = $this->randomMachineName(8);
+      $edit = [
+        'id' => $block_id,
+        'settings[label]' => $title,
+      ];
+      // Create the block using the link parsed from the library page.
+      $this->drupalGet($this->getAbsoluteUrl($link->getAttribute('href')));
+      $this->submitForm($edit, 'Save block');
+
+      // Ensure that the block was created with the expected weight.
+      /** @var \Drupal\block\BlockInterface $block */
+      $block = Block::load($block_id);
+      $this->assertEquals($weight, $block->getWeight(), 'Found the block with expected weight.');
+    }
+  }
+
+  /**
+   * Tests configuring and moving a module-define block to specific regions.
+   */
+  public function testBlock(): void {
+    // Place page title block to test error messages.
+    $this->drupalPlaceBlock('page_title_block');
+
+    // Disable the block.
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Disable');
+
+    // Select the 'Powered by Drupal' block to be configured and moved.
+    $block = [];
+    $block['id'] = 'system_powered_by_block';
+    $block['settings[label]'] = $this->randomMachineName(8);
+    $block['settings[label_display]'] = TRUE;
+    $block['theme'] = $this->config('system.theme')->get('default');
+    $block['region'] = 'header';
+
+    // Set block title to confirm that interface works and override any custom
+    // titles.
+    $this->drupalGet('admin/structure/block/add/' . $block['id'] . '/' . $block['theme']);
+    $this->submitForm([
+      'settings[label]' => $block['settings[label]'],
+      'settings[label_display]' => $block['settings[label_display]'],
+      'id' => $block['id'],
+      'region' => $block['region'],
+    ], 'Save block');
+    $this->assertSession()->statusMessageContains('The block configuration has been saved.', 'status');
+    // Check to see if the block was created by checking its configuration.
+    $instance = Block::load($block['id']);
+
+    $this->assertEquals($block['settings[label]'], $instance->label(), 'Stored block title found.');
+
+    // Check whether the block can be moved to all available regions.
+    foreach ($this->regions as $region) {
+      $this->moveBlockToRegion($block, $region);
+    }
+
+    // Disable the block.
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Disable');
+
+    // Confirm that the block is now listed as disabled.
+    $this->assertSession()->statusMessageContains('The block settings have been updated.', 'status');
+
+    // Confirm that the block instance title and markup are not displayed.
+    $this->drupalGet('node');
+    $this->assertSession()->pageTextNotContains($block['settings[label]']);
+    // Check for <div id="block-my-block-instance-name"> if the machine name
+    // is my_block_instance_name.
+    $xpath = $this->assertSession()->buildXPathQuery('//div[@id=:id]/*', [':id' => 'block-' . str_replace('_', '-', strtolower($block['id']))]);
+    $this->assertSession()->elementNotExists('xpath', $xpath);
+
+    $pages = [
+      '',
+      '<front>',
+      '/valid-page',
+      'user/login',
+    ];
+    // Test error when not including forward slash.
+    $this->drupalGet('admin/structure/block/manage/' . $block['id']);
+    $this->submitForm(['visibility[request_path][pages]' => implode("\n", $pages)], 'Save block');
+    $this->assertSession()->pageTextContains('The path user/login requires a leading forward slash when used with the Pages setting.');
+
+    // Test deleting the block from the edit form.
+    $this->drupalGet('admin/structure/block/manage/' . $block['id']);
+    $this->clickLink('Remove block');
+    $this->assertSession()->pageTextContains('Are you sure you want to remove the block ' . $block['settings[label]'] . ' from the Footer region?');
+    $this->submitForm([], 'Remove');
+    $this->assertSession()->statusMessageContains('The block ' . $block['settings[label]'] . ' has been removed from the Footer region.', 'status');
+
+    // Test deleting a block via "Configure block" link.
+    $block = $this->drupalPlaceBlock('system_powered_by_block', [
+      'region' => 'left_sidebar',
+    ]);
+    $this->drupalGet('admin/structure/block/manage/' . $block->id(), ['query' => ['destination' => 'admin']]);
+    $this->clickLink('Remove block');
+    $this->assertSession()->pageTextContains('Are you sure you want to remove the block ' . $block->label() . ' from the Left sidebar region?');
+    $this->submitForm([], 'Remove');
+    $this->assertSession()->statusMessageContains('The block ' . $block->label() . ' has been removed from the Left sidebar region.', 'status');
+    $this->assertSession()->addressEquals('admin');
+    $this->assertSession()->responseNotContains($block->id());
+  }
+
+  /**
+   * Tests that the block form has a theme selector when not passed via the URL.
+   */
+  public function testBlockThemeSelector(): void {
+    // Install all themes.
+    $themes = [
+      'olivero',
+      'claro',
+      'stark',
+    ];
+    \Drupal::service('theme_installer')->install($themes);
+    $theme_settings = $this->config('system.theme');
+    foreach ($themes as $theme) {
+      $this->drupalGet('admin/structure/block/list/' . $theme);
+      $this->assertSession()->titleEquals('Block layout | Drupal');
+      // Select the 'Powered by Drupal' block to be placed.
+      $block = [];
+      $block['id'] = $this->randomMachineName();
+      $block['theme'] = $theme;
+      $block['region'] = 'content';
+      $this->drupalGet('admin/structure/block/add/system_powered_by_block');
+      $this->submitForm($block, 'Save block');
+      $this->assertSession()->statusMessageContains('The block configuration has been saved.', 'status');
+      $this->assertSession()->addressEquals('admin/structure/block/list/' . $theme . '?block-placement=' . Html::getClass($block['id']));
+
+      // Set the default theme and ensure the block is placed.
+      $theme_settings->set('default', $theme)->save();
+      $this->drupalGet('');
+      $block_id = Html::getUniqueId('block-' . $block['id']);
+      $this->assertSession()->elementExists('xpath', "//div[@id = '$block_id']");
+    }
+  }
+
+  /**
+   * Tests block display of theme titles.
+   */
+  public function testThemeName(): void {
+    // Enable the help block.
+    $this->drupalPlaceBlock('help_block', ['region' => 'help']);
+    $this->drupalPlaceBlock('local_tasks_block');
+    // Explicitly set the default and admin themes.
+    $theme = 'block_test_special_chars_theme';
+    \Drupal::service('theme_installer')->install([$theme]);
+    $this->drupalGet('admin/structure/block');
+    $this->assertSession()->assertEscaped('<"Cat" & \'Mouse\'>');
+    $this->drupalGet('admin/structure/block/list/block_test_special_chars_theme');
+    $this->assertSession()->assertEscaped('Demonstrate block regions (<"Cat" & \'Mouse\'>)');
+  }
+
+  /**
+   * Tests block title display settings.
+   */
+  public function testHideBlockTitle(): void {
+    $block_name = 'system_powered_by_block';
+    // Create a random title for the block.
+    $title = $this->randomMachineName(8);
+    $id = $this->randomMachineName(8);
+    // Enable a standard block.
+    $default_theme = $this->config('system.theme')->get('default');
+    $edit = [
+      'id' => $id,
+      'region' => 'sidebar_first',
+      'settings[label]' => $title,
+    ];
+    $this->drupalGet('admin/structure/block/add/' . $block_name . '/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+    $this->assertSession()->statusMessageContains('The block configuration has been saved.', 'status');
+
+    // Confirm that the block is not displayed by default.
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextNotContains($title);
+
+    $edit = [
+      'settings[label_display]' => TRUE,
+    ];
+    $this->drupalGet('admin/structure/block/manage/' . $id);
+    $this->submitForm($edit, 'Save block');
+    $this->assertSession()->statusMessageContains('The block configuration has been saved.', 'status');
+
+    $this->drupalGet('admin/structure/block/manage/' . $id);
+    $this->assertSession()->checkboxChecked('edit-settings-label-display');
+
+    // Confirm that the block is displayed when enabled.
+    $this->drupalGet('user');
+    $this->assertSession()->pageTextContains($title);
+  }
+
+  /**
+   * Moves a block to a given region via the UI and confirms the result.
+   *
+   * @param array $block
+   *   An array of information about the block, including the following keys:
+   *   - module: The module providing the block.
+   *   - title: The title of the block.
+   *   - delta: The block's delta key.
+   * @param string $region
+   *   The machine name of the theme region to move the block to, for example
+   *   'header' or 'sidebar_first'.
+   */
+  public function moveBlockToRegion(array $block, $region): void {
+    // Set the created block to a specific region.
+    $block += ['theme' => $this->config('system.theme')->get('default')];
+    $edit = [];
+    $edit['blocks[' . $block['id'] . '][region]'] = $region;
+    $this->drupalGet('admin/structure/block');
+    $this->submitForm($edit, 'Save blocks');
+
+    // Confirm that the block was moved to the proper region.
+    $this->assertSession()->statusMessageContains('The block settings have been updated.', 'status');
+
+    // Confirm that the block is being displayed.
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains($block['settings[label]']);
+
+    $region_xpath = [
+      'header' => '//header[@role = "banner"]',
+      'sidebar_first' => '//aside[contains(@class, "layout-sidebar-first")]',
+      'content' => '//div[contains(@class, "layout-content")]',
+      'sidebar_second' => '//aside[contains(@class, "layout-sidebar-second")]',
+      'footer' => '//footer[@role = "contentinfo"]',
+    ];
+
+    // Confirm that the content block was found at the proper region.
+    $xpath = $this->assertSession()->buildXPathQuery($region_xpath[$region] . '//div[@id=:block-id]/*', [
+      ':block-id' => 'block-' . str_replace('_', '-', strtolower($block['id'])),
+    ]);
+    $this->assertSession()->elementExists('xpath', $xpath);
+  }
+
+  /**
+   * Tests that cache tags are properly set and bubbled up to the page cache.
+   *
+   * Verify that invalidation of these cache tags works:
+   * - "block:<block ID>"
+   * - "block_plugin:<block plugin ID>"
+   */
+  public function testBlockCacheTags(): void {
+    // The page cache only works for anonymous users.
+    $this->drupalLogout();
+
+    // Enable page caching.
+    $config = $this->config('system.performance');
+    $config->set('cache.page.max_age', 300);
+    $config->save();
+
+    // Place the "Powered by Drupal" block.
+    $block = $this->drupalPlaceBlock('system_powered_by_block', ['id' => 'powered']);
+
+    // Prime the page cache.
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
+
+    // Verify a cache hit, but also the presence of the correct cache tags in
+    // both the page and block caches.
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');
+    $cid_parts = [Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString(), ''];
+    $cid = implode(':', $cid_parts);
+    $cache_entry = \Drupal::cache('page')->get($cid);
+    $expected_cache_tags = [
+      'config:block_list',
+      'block_view',
+      'config:block.block.powered',
+      'config:user.role.anonymous',
+      'http_response',
+      'rendered',
+    ];
+    sort($expected_cache_tags);
+    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions'])->getKeys();
+    $this->assertSame($expected_cache_tags, $cache_entry->tags);
+    $cache_entry = \Drupal::cache('render')->get('entity_view:block:powered:' . implode(':', $keys));
+    $expected_cache_tags = [
+      'block_view',
+      'config:block.block.powered',
+      'rendered',
+    ];
+    sort($expected_cache_tags);
+    $this->assertSame($expected_cache_tags, $cache_entry->tags);
+
+    // The "Powered by Drupal" block is modified; verify a cache miss.
+    $block->setRegion('content');
+    $block->save();
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
+
+    // Now we should have a cache hit again.
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');
+
+    // Place the "Powered by Drupal" block another time; verify a cache miss.
+    $this->drupalPlaceBlock('system_powered_by_block', ['id' => 'powered_2']);
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
+
+    // Verify a cache hit, but also the presence of the correct cache tags.
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');
+    $cid_parts = [Url::fromRoute('<front>', [], ['absolute' => TRUE])->toString(), ''];
+    $cid = implode(':', $cid_parts);
+    $cache_entry = \Drupal::cache('page')->get($cid);
+    $expected_cache_tags = [
+      'config:block_list',
+      'block_view',
+      'config:block.block.powered',
+      'config:block.block.powered_2',
+      'config:user.role.anonymous',
+      'http_response',
+      'rendered',
+    ];
+    sort($expected_cache_tags);
+    $this->assertEquals($expected_cache_tags, $cache_entry->tags);
+    $expected_cache_tags = [
+      'block_view',
+      'config:block.block.powered',
+      'rendered',
+    ];
+    sort($expected_cache_tags);
+    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions'])->getKeys();
+    $cache_entry = \Drupal::cache('render')->get('entity_view:block:powered:' . implode(':', $keys));
+    $this->assertSame($expected_cache_tags, $cache_entry->tags);
+    $expected_cache_tags = [
+      'block_view',
+      'config:block.block.powered_2',
+      'rendered',
+    ];
+    sort($expected_cache_tags);
+    $keys = \Drupal::service('cache_contexts_manager')->convertTokensToKeys(['languages:language_interface', 'theme', 'user.permissions'])->getKeys();
+    $cache_entry = \Drupal::cache('render')->get('entity_view:block:powered_2:' . implode(':', $keys));
+    $this->assertSame($expected_cache_tags, $cache_entry->tags);
+
+    // Now we should have a cache hit again.
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'HIT');
+
+    // Delete the "Powered by Drupal" blocks; verify a cache miss.
+    $block_storage = \Drupal::entityTypeManager()->getStorage('block');
+    $block_storage->load('powered')->delete();
+    $block_storage->load('powered_2')->delete();
+    $this->drupalGet('<front>');
+    $this->assertSession()->responseHeaderEquals('X-Drupal-Cache', 'MISS');
+  }
+
+  /**
+   * Tests that a link exists to block layout from the appearance form.
+   */
+  public function testThemeAdminLink(): void {
+    $this->drupalPlaceBlock('help_block', ['region' => 'help']);
+    $theme_admin = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+      'access administration pages',
+    ]);
+    $this->drupalLogin($theme_admin);
+    $this->drupalGet('admin/appearance');
+    $this->assertSession()->pageTextContains('You can place blocks for each theme on the block layout page');
+    $this->assertSession()->linkByHrefExists('admin/structure/block');
+  }
+
+  /**
+   * Tests that uninstalling a theme removes its block configuration.
+   */
+  public function testUninstallTheme(): void {
+    /** @var \Drupal\Core\Extension\ThemeInstallerInterface $theme_installer */
+    $theme_installer = \Drupal::service('theme_installer');
+
+    $theme_installer->install(['claro']);
+    $this->config('system.theme')->set('default', 'claro')->save();
+    $block = $this->drupalPlaceBlock('system_powered_by_block', ['theme' => 'claro', 'region' => 'help']);
+    $this->drupalGet('<front>');
+    $this->assertSession()->pageTextContains('Powered by Drupal');
+
+    $this->config('system.theme')->set('default', 'stark')->save();
+    $theme_installer->uninstall(['claro']);
+
+    // Ensure that the block configuration does not exist anymore.
+    $this->assertNull(Block::load($block->id()));
+  }
+
+  /**
+   * Tests the block access.
+   */
+  public function testBlockAccess(): void {
+    $this->drupalPlaceBlock('test_access', ['region' => 'help']);
+
+    $this->drupalGet('<front>');
+    $this->assertSession()->pageTextNotContains('Hello test world');
+
+    \Drupal::keyValue('block_test')->set('access', TRUE);
+    $this->drupalGet('<front>');
+    $this->assertSession()->pageTextContains('Hello test world');
+  }
+
+  /**
+   * Tests block_user_role_delete.
+   */
+  public function testBlockUserRoleDelete(): void {
+    $role1 = Role::create(['id' => 'test_role1', 'label' => 'Test role 1']);
+    $role1->save();
+
+    $role2 = Role::create(['id' => 'test_role2', 'label' => 'Test role 2']);
+    $role2->save();
+
+    $block = Block::create([
+      'id' => $this->randomMachineName(),
+      'plugin' => 'system_powered_by_block',
+      'theme' => 'stark',
+    ]);
+
+    $block->setVisibilityConfig('user_role', [
+      'roles' => [
+        $role1->id() => $role1->id(),
+        $role2->id() => $role2->id(),
+      ],
+    ]);
+
+    $block->save();
+
+    $this->assertEquals([$role1->id() => $role1->id(), $role2->id() => $role2->id()], $block->getVisibility()['user_role']['roles']);
+
+    $role1->delete();
+
+    $block = Block::load($block->id());
+    $this->assertEquals([$role2->id() => $role2->id()], $block->getVisibility()['user_role']['roles']);
+  }
+
+  /**
+   * Tests block title.
+   */
+  public function testBlockTitle(): void {
+    // Create a custom title for the block.
+    $title = "This block's <b>great!</b>";
+    // Enable a standard block.
+    $default_theme = $this->config('system.theme')->get('default');
+    $edit = [
+      'id' => 'test',
+      'region' => 'sidebar_first',
+      'settings[label]' => $title,
+      'settings[label_display]' => TRUE,
+    ];
+    // Set the block to be shown only to authenticated users.
+    $edit['visibility[user_role][roles][' . RoleInterface::AUTHENTICATED_ID . ']'] = TRUE;
+    $this->drupalGet('admin/structure/block/add/foo/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    // Ensure that the title is displayed as plain text.
+    $elements = $this->xpath('//table/tbody/tr//td[contains(@class, "block")]');
+    $this->assertEquals($title, $elements[0]->getText());
+
+    $this->clickLink('Disable');
+    $elements = $this->xpath('//table/tbody/tr//td[contains(@class, "block")]');
+    $this->assertEquals("$title (disabled)", $elements[0]->getText());
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockTestBase.php

@@ -0,0 +1,80 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\filter\Entity\FilterFormat;
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Provides setup and helper methods for block module tests.
+ */
+abstract class BlockTestBase extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'filter',
+    'test_page_test',
+    'help',
+    'block_test',
+  ];
+
+  /**
+   * A list of theme regions to test.
+   *
+   * @var array
+   */
+  protected $regions;
+
+  /**
+   * A test user with administrative privileges.
+   *
+   * @var \Drupal\user\UserInterface
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Use the test page as the front page.
+    $this->config('system.site')->set('page.front', '/test-page')->save();
+
+    // Create Full HTML text format.
+    $full_html_format = FilterFormat::create([
+      'format' => 'full_html',
+      'name' => 'Full HTML',
+    ]);
+    $full_html_format->save();
+
+    // Create and log in an administrative user having access to the Full HTML
+    // text format.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      $full_html_format->getPermissionName(),
+      'access administration pages',
+    ]);
+    $this->drupalLogin($this->adminUser);
+
+    // Define the existing regions.
+    $this->regions = [
+      'header',
+      'sidebar_first',
+      'content',
+      'sidebar_second',
+      'footer',
+    ];
+    $block_storage = $this->container->get('entity_type.manager')->getStorage('block');
+    $blocks = $block_storage->loadByProperties(['theme' => $this->config('system.theme')->get('default')]);
+    foreach ($blocks as $block) {
+      $block->delete();
+    }
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockUiTest.php

@@ -0,0 +1,414 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Component\Utility\Html;
+use Drupal\language\Entity\ConfigurableLanguage;
+use Drupal\language\Plugin\LanguageNegotiation\LanguageNegotiationUrl;
+use Drupal\Tests\BrowserTestBase;
+
+// cspell:ignore displaymessage scriptalertxsssubjectscript
+// cspell:ignore testcontextawareblock
+
+/**
+ * Tests that the block configuration UI exists and stores data correctly.
+ *
+ * @group block
+ */
+class BlockUiTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'block_test',
+    'help',
+    'condition_test',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * The submitted block values used by this test.
+   *
+   * @var array
+   */
+  protected $blockValues;
+
+  /**
+   * The block entities used by this test.
+   *
+   * @var \Drupal\block\BlockInterface[]
+   */
+  protected $blocks;
+
+  /**
+   * An administrative user to configure the test environment.
+   *
+   * @var \Drupal\user\Entity\User|false
+   */
+  protected $adminUser;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    // Create and log in an administrative user.
+    $this->adminUser = $this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]);
+    $this->drupalLogin($this->adminUser);
+
+    // Enable some test blocks.
+    $this->blockValues = [
+      [
+        'label' => 'Tools',
+        'tr' => '6',
+        'plugin_id' => 'system_menu_block:tools',
+        'settings' => ['region' => 'sidebar_second', 'id' => 'tools'],
+        'test_weight' => '-1',
+      ],
+      [
+        'label' => 'Powered by Drupal',
+        'tr' => '17',
+        'plugin_id' => 'system_powered_by_block',
+        'settings' => ['region' => 'footer', 'id' => 'powered'],
+        'test_weight' => '0',
+      ],
+    ];
+    $this->blocks = [];
+    foreach ($this->blockValues as $values) {
+      $this->blocks[] = $this->drupalPlaceBlock($values['plugin_id'], $values['settings']);
+    }
+  }
+
+  /**
+   * Tests block demo page exists and functions correctly.
+   */
+  public function testBlockDemoUiPage(): void {
+    $this->drupalPlaceBlock('help_block', ['region' => 'help']);
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Demonstrate block regions (Stark)');
+    $this->assertSession()->elementExists('xpath', '//header[@role = "banner"]/div/div[contains(@class, "block-region") and contains(text(), "Header")]');
+
+    // Ensure that other themes can use the block demo page.
+    \Drupal::service('theme_installer')->install(['test_theme']);
+    $this->drupalGet('admin/structure/block/demo/test_theme');
+    $this->assertSession()->assertEscaped('<strong>Test theme</strong>');
+
+    // Ensure that a hidden theme cannot use the block demo page.
+    \Drupal::service('theme_installer')->install(['stable9']);
+    $this->drupalGet('admin/structure/block/demo/stable9');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Delete all blocks and verify saving the block layout results in a
+    // validation error.
+    $block_storage = \Drupal::service('entity_type.manager')->getStorage('block');
+    $blocks = $block_storage->loadMultiple();
+    foreach ($blocks as $block) {
+      $block->delete();
+    }
+    $this->drupalGet('admin/structure/block');
+    $blocks_table = $this->xpath("//tr[@class='block-enabled']");
+    $this->assertEmpty($blocks_table, 'The blocks table is now empty.');
+    $this->submitForm([], 'Save blocks');
+    $this->assertSession()->pageTextContains('No blocks settings to update');
+
+  }
+
+  /**
+   * Tests block admin page exists and functions correctly.
+   */
+  public function testBlockAdminUiPage(): void {
+    // Visit the blocks admin ui.
+    $this->drupalGet('admin/structure/block');
+    // Look for the blocks table.
+    $this->assertSession()->elementExists('xpath', "//table[@id='blocks']");
+    // Look for test blocks in the table.
+    foreach ($this->blockValues as $delta => $values) {
+      $block = $this->blocks[$delta];
+      $label = $block->label();
+      $this->assertSession()->elementTextEquals('xpath', '//*[@id="blocks"]/tbody/tr[' . $values['tr'] . ']/td[1]/text()', $label);
+      // Look for a test block region select form element.
+      $this->assertSession()->fieldExists('blocks[' . $values['settings']['id'] . '][region]');
+      // Move the test block to the header region.
+      $edit['blocks[' . $values['settings']['id'] . '][region]'] = 'header';
+      // Look for a test block weight select form element.
+      $this->assertSession()->fieldExists('blocks[' . $values['settings']['id'] . '][weight]');
+      // Change the test block's weight.
+      $edit['blocks[' . $values['settings']['id'] . '][weight]'] = $values['test_weight'];
+    }
+    $this->drupalGet('admin/structure/block');
+    $this->submitForm($edit, 'Save blocks');
+    foreach ($this->blockValues as $values) {
+      // Check if the region and weight settings changes have persisted.
+      $this->assertTrue($this->assertSession()->optionExists('edit-blocks-' . $values['settings']['id'] . '-region', 'header')->isSelected());
+      $this->assertTrue($this->assertSession()->optionExists('edit-blocks-' . $values['settings']['id'] . '-weight', $values['test_weight'])->isSelected());
+    }
+
+    // Add a block with a machine name the same as a region name.
+    $this->drupalPlaceBlock('system_powered_by_block', ['region' => 'header', 'id' => 'header']);
+    $this->drupalGet('admin/structure/block');
+    $this->assertSession()->elementExists('xpath', '//tr[contains(@class, "region-title-header")]');
+
+    // Ensure hidden themes do not appear in the UI. Enable another non base
+    // theme and place the local tasks block.
+    $this->assertTrue(\Drupal::service('theme_handler')->themeExists('stark'), 'The stark base theme is enabled');
+    $this->drupalPlaceBlock('local_tasks_block', ['region' => 'header', 'theme' => 'stark']);
+    // We have to enable at least one extra theme that is not hidden so that
+    // local tasks will show up. That's why we enable test_theme_theme.
+    \Drupal::service('theme_installer')->install(['stable9', 'test_theme_theme']);
+    $this->drupalGet('admin/structure/block');
+    $theme_handler = \Drupal::service('theme_handler');
+    $this->assertSession()->linkExists($theme_handler->getName('stark'));
+    $this->assertSession()->linkExists($theme_handler->getName('test_theme_theme'));
+    $this->assertSession()->linkNotExists($theme_handler->getName('stable9'));
+
+    // Ensure that a hidden theme cannot use the block demo page.
+    $this->drupalGet('admin/structure/block/list/stable9');
+    $this->assertSession()->statusCodeEquals(404);
+
+    // Ensure that a hidden theme set as the admin theme can use the block demo
+    // page.
+    \Drupal::configFactory()->getEditable('system.theme')->set('admin', 'stable9')->save();
+    \Drupal::service('router.builder')->rebuildIfNeeded();
+    $this->drupalPlaceBlock('local_tasks_block', ['region' => 'header', 'theme' => 'stable9']);
+    $this->drupalGet('admin/structure/block');
+    $this->assertSession()->linkExists($theme_handler->getName('stable9'));
+    $this->drupalGet('admin/structure/block/list/stable9');
+    $this->assertSession()->statusCodeEquals(200);
+  }
+
+  /**
+   * Tests the block categories on the listing page.
+   */
+  public function testCandidateBlockList(): void {
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Place block');
+    $this->assertSession()->elementExists('xpath', '//tr[.//td/div[text()="Display message"] and .//td[text()="Block test"] and .//td//a[contains(@href, "admin/structure/block/add/test_block_instantiation/stark")]]');
+
+    // Trigger the custom category addition in block_test_block_alter().
+    $this->container->get('state')->set('block_test_info_alter', TRUE);
+    $this->container->get('plugin.manager.block')->clearCachedDefinitions();
+
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Place block');
+    $this->assertSession()->elementExists('xpath', '//tr[.//td/div[text()="Display message"] and .//td[text()="Custom category"] and .//td//a[contains(@href, "admin/structure/block/add/test_block_instantiation/stark")]]');
+  }
+
+  /**
+   * Tests the behavior of unsatisfied context-aware blocks.
+   */
+  public function testContextAwareUnsatisfiedBlocks(): void {
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Place block');
+    // Verify that the context-aware test block does not appear.
+    $this->assertSession()->elementNotExists('xpath', '//tr[.//td/div[text()="Test context-aware unsatisfied block"] and .//td[text()="Block test"] and .//td//a[contains(@href, "admin/structure/block/add/test_context_aware_unsatisfied/stark")]]');
+
+    $definition = \Drupal::service('plugin.manager.block')->getDefinition('test_context_aware_unsatisfied');
+    $this->assertNotEmpty($definition, 'The context-aware test block does not exist.');
+  }
+
+  /**
+   * Tests the behavior of context-aware blocks.
+   */
+  public function testContextAwareBlocks(): void {
+    $expected_text = '<div id="test_context_aware--username">' . \Drupal::currentUser()->getAccountName() . '</div>';
+    $this->drupalGet('');
+    $this->assertSession()->pageTextNotContains('Test context-aware block');
+    $this->assertSession()->responseNotContains($expected_text);
+
+    $block_url = 'admin/structure/block/add/test_context_aware/stark';
+
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Place block');
+    $this->assertSession()->elementExists('xpath', '//tr[.//td/div[text()="Test context-aware block"] and .//td[text()="Block test"] and .//td//a[contains(@href, "' . $block_url . '")]]');
+    $definition = \Drupal::service('plugin.manager.block')->getDefinition('test_context_aware');
+    $this->assertNotEmpty($definition, 'The context-aware test block exists.');
+    $edit = [
+      'region' => 'content',
+      'settings[context_mapping][user]' => '@block_test.multiple_static_context:userB',
+    ];
+    $this->drupalGet($block_url);
+    $this->submitForm($edit, 'Save block');
+
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('Test context-aware block');
+    $this->assertSession()->pageTextContains('User context found.');
+    $this->assertSession()->responseContains($expected_text);
+
+    // Test context mapping form element is not visible if there are no valid
+    // context options for the block (the
+    // test_context_aware_no_valid_context_options block has one context defined
+    // which is not available for it on the Block Layout interface).
+    $this->drupalGet('admin/structure/block/add/test_context_aware_no_valid_context_options/stark');
+    $this->assertSession()->fieldNotExists('edit-settings-context-mapping-email');
+
+    // Test context mapping allows empty selection for optional contexts.
+    $this->drupalGet('admin/structure/block/manage/stark_testcontextawareblock');
+    $edit = [
+      'settings[context_mapping][user]' => '',
+    ];
+    $this->submitForm($edit, 'Save block');
+    $this->drupalGet('');
+    $this->assertSession()->pageTextContains('No context mapping selected.');
+    $this->assertSession()->pageTextNotContains('User context found.');
+
+    // Tests that conditions with missing context are not displayed.
+    $this->drupalGet('admin/structure/block/manage/stark_testcontextawareblock');
+    $this->assertSession()->responseNotContains('No existing type');
+    $this->assertSession()->elementNotExists('xpath', '//*[@name="visibility[condition_test_no_existing_type][negate]"]');
+  }
+
+  /**
+   * Tests that the BlockForm populates machine name correctly.
+   */
+  public function testMachineNameSuggestion(): void {
+    // Check the form uses the raw machine name suggestion when no instance
+    // already exists.
+    $url = 'admin/structure/block/add/test_block_instantiation/stark';
+    $this->drupalGet($url);
+    $this->assertSession()->fieldValueEquals('id', 'stark_displaymessage');
+    $edit = ['region' => 'content'];
+    $this->drupalGet($url);
+    $this->submitForm($edit, 'Save block');
+    $this->assertSession()->pageTextContains('The block configuration has been saved.');
+
+    // Now, check to make sure the form starts by auto-incrementing correctly.
+    $this->drupalGet($url);
+    $this->assertSession()->fieldValueEquals('id', 'stark_displaymessage_2');
+    $this->drupalGet($url);
+    $this->submitForm($edit, 'Save block');
+    $this->assertSession()->pageTextContains('The block configuration has been saved.');
+
+    // And verify that it continues working beyond just the first two.
+    $this->drupalGet($url);
+    $this->assertSession()->fieldValueEquals('id', 'stark_displaymessage_3');
+  }
+
+  /**
+   * Tests the block placement indicator.
+   */
+  public function testBlockPlacementIndicator(): void {
+    // Test the block placement indicator with using the domain as URL language
+    // indicator. This causes destination query parameters to be absolute URLs.
+    \Drupal::service('module_installer')->install(['language', 'locale']);
+    $this->container = \Drupal::getContainer();
+    ConfigurableLanguage::createFromLangcode('it')->save();
+    $config = $this->config('language.types');
+    $config->set('negotiation.language_interface.enabled', [
+      LanguageNegotiationUrl::METHOD_ID => -10,
+    ]);
+    $config->save();
+    $config = $this->config('language.negotiation');
+    $config->set('url.source', LanguageNegotiationUrl::CONFIG_DOMAIN);
+    $config->set('url.domains', [
+      'en' => \Drupal::request()->getHost(),
+      'it' => 'it.example.com',
+    ]);
+    $config->save();
+
+    // Select the 'Powered by Drupal' block to be placed.
+    $block = [];
+    $block['id'] = $this->randomMachineName();
+    $block['theme'] = 'stark';
+    $block['region'] = 'content';
+
+    // After adding a block, it will indicate which block was just added.
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block');
+    $this->submitForm($block, 'Save block');
+    $this->assertSession()->addressEquals('admin/structure/block/list/stark?block-placement=' . Html::getClass($block['id']));
+
+    // Resaving the block page will remove the block placement indicator.
+    $this->submitForm([], 'Save blocks');
+    $this->assertSession()->addressEquals('admin/structure/block/list/stark');
+
+    // Place another block and test the remove functionality works with the
+    // block placement indicator. Click the first 'Place block' link to bring up
+    // the list of blocks to place in the first available region.
+    $this->clickLink('Place block');
+    // Select the first available block, which is the 'test_block_instantiation'
+    // plugin, with a default machine name 'stark-displaymessage' that is used
+    // for the 'block-placement' querystring parameter.
+    $this->clickLink('Place block');
+    $this->submitForm([], 'Save block');
+    $this->assertSession()->addressEquals('admin/structure/block/list/stark?block-placement=stark-displaymessage');
+
+    // Removing a block will remove the block placement indicator.
+    $this->clickLink('Remove');
+    $this->submitForm([], 'Remove');
+    $this->assertSession()->addressEquals('admin/structure/block/list/stark');
+  }
+
+  /**
+   * Tests if validation errors are passed plugin form to the parent form.
+   */
+  public function testBlockValidateErrors(): void {
+    $this->drupalGet('admin/structure/block/add/test_settings_validation/stark');
+    $this->submitForm([
+      'region' => 'content',
+      'settings[digits]' => 'abc',
+    ], 'Save block');
+
+    $this->assertSession()->statusMessageContains('Only digits are allowed', 'error');
+    $this->assertSession()->elementExists('xpath', '//div[contains(@class,"form-item-settings-digits")]/input[contains(@class,"error")]');
+  }
+
+  /**
+   * Tests that the enable/disable routes are protected from CSRF.
+   */
+  public function testRouteProtection(): void {
+    // Get the first block generated in our setUp method.
+    /** @var \Drupal\block\BlockInterface $block */
+    $block = reset($this->blocks);
+    // Ensure that the enable and disable routes are protected.
+    $this->drupalGet('admin/structure/block/manage/' . $block->id() . '/disable');
+    $this->assertSession()->statusCodeEquals(403);
+    $this->drupalGet('admin/structure/block/manage/' . $block->id() . '/enable');
+    $this->assertSession()->statusCodeEquals(403);
+  }
+
+  /**
+   * Tests that users without permission are not able to view broken blocks.
+   */
+  public function testBrokenBlockVisibility(): void {
+    $assert_session = $this->assertSession();
+
+    $block = $this->drupalPlaceBlock('broken');
+
+    // Ensure that broken block configuration can be accessed.
+    $this->drupalGet('admin/structure/block/manage/' . $block->id());
+    $assert_session->statusCodeEquals(200);
+
+    // Login as an admin user to the site.
+    $this->drupalLogin($this->adminUser);
+    $this->drupalGet('');
+    $assert_session->statusCodeEquals(200);
+    // Check that this user can view the Broken Block message.
+    $assert_session->pageTextContains('This block is broken or missing. You may be missing content or you might need to install the original module.');
+    $this->drupalLogout();
+
+    // Visit the same page as anonymous.
+    $this->drupalGet('');
+    $assert_session->statusCodeEquals(200);
+    // Check that this user cannot view the Broken Block message.
+    $assert_session->pageTextNotContains('This block is broken or missing. You may be missing content or you might need to install the original module.');
+
+    // Visit same page as an authorized user that does not have access to
+    // administer blocks.
+    $this->drupalLogin($this->drupalCreateUser(['access administration pages']));
+    $this->drupalGet('');
+    $assert_session->statusCodeEquals(200);
+    // Check that this user cannot view the Broken Block message.
+    $assert_session->pageTextNotContains('This block is broken or missing. You may be missing content or you might need to install the original module.');
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockWeightUpdateTest.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\block\Entity\Block;
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * @covers block_post_update_make_weight_integer
+ * @group block
+ */
+class BlockWeightUpdateTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles() {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../system/tests/fixtures/update/drupal-10.3.0.filled.standard.php.gz',
+    ];
+  }
+
+  /**
+   * Tests update path for blocks' `weight` property.
+   */
+  public function testRunUpdates() {
+    // Find a block and change it to have a null weight.
+    /** @var \Drupal\Core\Database\Connection $database */
+    $database = $this->container->get('database');
+    $block = $database->select('config', 'c')
+      ->fields('c', ['data'])
+      ->condition('name', 'block.block.claro_content')
+      ->execute()
+      ->fetchField();
+    $block = unserialize($block);
+    $block['weight'] = NULL;
+    $database->update('config')
+      ->fields([
+        'data' => serialize($block),
+      ])
+      ->condition('name', 'block.block.claro_content')
+      ->execute();
+
+    $this->assertNull(Block::load('claro_content')->get('weight'));
+    $this->runUpdates();
+    $this->assertSame(0, Block::load('claro_content')->get('weight'));
+  }
+
+}

web/core/modules/block/tests/src/Functional/BlockXssTest.php

@@ -0,0 +1,176 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\block_content\Entity\BlockContent;
+use Drupal\block_content\Entity\BlockContentType;
+use Drupal\Core\Url;
+use Drupal\system\Entity\Menu;
+use Drupal\Tests\BrowserTestBase;
+use Drupal\views\Entity\View;
+
+/**
+ * Tests that the block module properly escapes block descriptions.
+ *
+ * @group block
+ */
+class BlockXssTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_content', 'menu_ui', 'views'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests that nothing is escaped other than the blocks explicitly tested.
+   */
+  public function testNoUnexpectedEscaping(): void {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]));
+    $this->drupalGet(Url::fromRoute('block.admin_display'));
+    $this->clickLink('Place block');
+    $this->assertSession()->assertNoEscaped('<');
+  }
+
+  /**
+   * Tests XSS in title.
+   */
+  public function testXssInTitle(): void {
+    $this->drupalPlaceBlock('system_powered_by_block', [
+      'label' => '<script>alert("XSS label");</script>',
+      'label_display' => 'visible',
+    ]);
+
+    $this->drupalGet('');
+    // Check that the block title was properly sanitized when rendered.
+    $this->assertSession()->assertEscaped('<script>alert("XSS label");</script>');
+    $this->assertSession()->responseNotContains('<script>alert("XSS label");</script>');
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]));
+    $default_theme = $this->config('system.theme')->get('default');
+    $this->drupalGet('admin/structure/block/list/' . $default_theme);
+    // Check that the block title was properly sanitized in Block Plugin UI
+    // Admin page.
+    $this->assertSession()->assertEscaped('<script>alert("XSS label");</script>');
+    $this->assertSession()->responseNotContains("<script>alert('XSS subject');</script>");
+  }
+
+  /**
+   * Tests various modules that provide blocks for XSS.
+   */
+  public function testBlockXss(): void {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+    ]));
+
+    $this->doViewTest();
+    $this->doMenuTest();
+    $this->doBlockContentTest();
+
+    $this->drupalGet(Url::fromRoute('block.admin_display'));
+    $this->clickLink('Place block');
+    // Check that the page does not have double escaped HTML tags.
+    $this->assertSession()->responseNotContains('&amp;lt;');
+  }
+
+  /**
+   * Tests XSS coming from View block labels.
+   */
+  protected function doViewTest(): void {
+    // Create a View without a custom label for its block Display. The
+    // admin_label of the block then becomes just the View's label.
+    $view = View::create([
+      'id' => $this->randomMachineName(),
+      'label' => '<script>alert("view1");</script>',
+    ]);
+    $view->addDisplay('block');
+    $view->save();
+
+    // Create a View with a custom label for its block Display. The
+    // admin_label of the block then becomes the View's label combined with
+    // the Display's label.
+    $view = View::create([
+      'id' => $this->randomMachineName(),
+      'label' => '<script>alert("view2");</script>',
+    ]);
+    $view->addDisplay('block', 'Fish & chips');
+    $view->save();
+
+    $this->drupalGet(Url::fromRoute('block.admin_display'));
+    $this->clickLink('Place block');
+
+    // \Drupal\views\Plugin\Derivative\ViewsBlock::getDerivativeDefinitions()
+    // has a different code path for an admin label based only on the View
+    // label versus one based on both the View label and the Display label.
+    // Ensure that this test is covering both code paths by asserting the
+    // absence of a ":" for the first View and the presence of a ":" for the
+    // second one. Note that the second assertion is redundant with the one
+    // further down which also checks for the Display label, but is included
+    // here for clarity.
+    $this->assertSession()->assertNoEscaped('<script>alert("view1");</script>:');
+    $this->assertSession()->assertEscaped('<script>alert("view2");</script>:');
+
+    // Assert that the blocks have their admin labels escaped and
+    // don't appear anywhere unescaped.
+    $this->assertSession()->assertEscaped('<script>alert("view1");</script>');
+    $this->assertSession()->responseNotContains('<script>alert("view1");</script>');
+    $this->assertSession()->assertEscaped('<script>alert("view2");</script>: Fish & chips');
+    $this->assertSession()->responseNotContains('<script>alert("view2");</script>');
+    $this->assertSession()->responseNotContains('Fish & chips');
+
+    // Assert the Display label doesn't appear anywhere double escaped.
+    $this->assertSession()->responseNotContains('Fish & chips');
+    $this->assertSession()->responseNotContains('Fish &amp;amp; chips');
+  }
+
+  /**
+   * Tests XSS coming from Menu block labels.
+   */
+  protected function doMenuTest(): void {
+    Menu::create([
+      'id' => $this->randomMachineName(),
+      'label' => '<script>alert("menu");</script>',
+    ])->save();
+
+    $this->drupalGet(Url::fromRoute('block.admin_display'));
+    $this->clickLink('Place block');
+
+    $this->assertSession()->assertEscaped('<script>alert("menu");</script>');
+    $this->assertSession()->responseNotContains('<script>alert("menu");</script>');
+  }
+
+  /**
+   * Tests XSS coming from Block Content block info.
+   */
+  protected function doBlockContentTest(): void {
+    BlockContentType::create([
+      'id' => 'basic',
+      'label' => 'basic',
+      'revision' => TRUE,
+    ])->save();
+    BlockContent::create([
+      'type' => 'basic',
+      'info' => '<script>alert("block_content");</script>',
+    ])->save();
+
+    $this->drupalGet(Url::fromRoute('block.admin_display'));
+    $this->clickLink('Place block');
+
+    $this->assertSession()->assertEscaped('<script>alert("block_content");</script>');
+    $this->assertSession()->responseNotContains('<script>alert("block_content");</script>');
+  }
+
+}

web/core/modules/block/tests/src/Functional/GenericTest.php

@@ -0,0 +1,14 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\system\Functional\Module\GenericModuleTestBase;
+
+/**
+ * Generic module test for block.
+ *
+ * @group block
+ */
+class GenericTest extends GenericModuleTestBase {}

web/core/modules/block/tests/src/Functional/NonDefaultBlockAdminTest.php

@@ -0,0 +1,51 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional;
+
+use Drupal\Tests\BrowserTestBase;
+
+/**
+ * Tests the block administration page for a non-default theme.
+ *
+ * @group block
+ */
+class NonDefaultBlockAdminTest extends BrowserTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->drupalPlaceBlock('local_tasks_block');
+  }
+
+  /**
+   * Tests non-default theme admin.
+   */
+  public function testNonDefaultBlockAdmin(): void {
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+      'administer themes',
+    ]);
+    $this->drupalLogin($admin_user);
+    $new_theme = 'olivero';
+    \Drupal::service('theme_installer')->install([$new_theme]);
+    // Ensure that the Olivero tab is shown.
+    $this->drupalGet('admin/structure/block/list/' . $new_theme);
+    $this->assertSession()->pageTextContains('Olivero');
+  }
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockJsonAnonTest.php

@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class BlockJsonAnonTest extends BlockResourceTestBase {
+
+  use AnonResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockJsonBasicAuthTest.php

@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class BlockJsonBasicAuthTest extends BlockResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockJsonCookieTest.php

@@ -0,0 +1,36 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+
+/**
+ * @group rest
+ */
+class BlockJsonCookieTest extends BlockResourceTestBase {
+
+  use CookieResourceTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'application/json';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockResourceTestBase.php

@@ -0,0 +1,173 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\block\Entity\Block;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Tests\rest\Functional\EntityResource\ConfigEntityResourceTestBase;
+
+/**
+ * Resource test base for the block entity.
+ */
+abstract class BlockResourceTestBase extends ConfigEntityResourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $entityTypeId = 'block';
+
+  /**
+   * @var \Drupal\block\BlockInterface
+   */
+  protected $entity;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUpAuthorization($method) {
+    switch ($method) {
+      case 'GET':
+        $this->entity->setVisibilityConfig('user_role', [])->save();
+        break;
+
+      case 'POST':
+        $this->grantPermissionsToTestedRole(['administer blocks']);
+        break;
+
+      case 'PATCH':
+        $this->grantPermissionsToTestedRole(['administer blocks']);
+        break;
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function createEntity() {
+    $block = Block::create([
+      'plugin' => 'llama_block',
+      'region' => 'header',
+      'id' => 'llama',
+      'theme' => 'stark',
+    ]);
+    // All blocks can be viewed by the anonymous user by default. An interesting
+    // side effect of this is that any anonymous user is also able to read the
+    // corresponding block config entity via REST, even if an authentication
+    // provider is configured for the block config entity REST resource! In
+    // other words: Block entities do not distinguish between 'view' as in
+    // "render on a page" and 'view' as in "read the configuration".
+    // This prevents that.
+    // @todo Fix this in https://www.drupal.org/node/2820315.
+    $block->setVisibilityConfig('user_role', [
+      'id' => 'user_role',
+      'roles' => ['non-existing-role' => 'non-existing-role'],
+      'negate' => FALSE,
+      'context_mapping' => [
+        'user' => '@user.current_user_context:current_user',
+      ],
+    ]);
+    $block->save();
+
+    return $block;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedNormalizedEntity() {
+    $normalization = [
+      'uuid' => $this->entity->uuid(),
+      'id' => 'llama',
+      'weight' => 0,
+      'langcode' => 'en',
+      'status' => TRUE,
+      'dependencies' => [
+        'theme' => [
+          'stark',
+        ],
+      ],
+      'theme' => 'stark',
+      'region' => 'header',
+      'provider' => NULL,
+      'plugin' => 'llama_block',
+      'settings' => [
+        'id' => 'broken',
+        'label' => '',
+        'provider' => 'core',
+        'label_display' => 'visible',
+      ],
+      'visibility' => [],
+    ];
+
+    return $normalization;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getNormalizedPostEntity() {
+    // @todo Update in https://www.drupal.org/node/2300677.
+    return [];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedCacheContexts() {
+    // @see ::createEntity()
+    return ['url.site'];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedCacheTags() {
+    // Because the 'user.permissions' cache context is missing, the cache tag
+    // for the anonymous user role is never added automatically.
+    return array_values(array_diff(parent::getExpectedCacheTags(), ['config:user.role.anonymous']));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedUnauthorizedAccessMessage($method) {
+    switch ($method) {
+      case 'GET':
+        return "The block visibility condition 'user_role' denied access.";
+
+      default:
+        return parent::getExpectedUnauthorizedAccessMessage($method);
+    }
+  }
+
+  /**
+   * {@inheritdoc}
+   *
+   * @todo Fix this in https://www.drupal.org/node/2820315.
+   */
+  protected function getExpectedUnauthorizedAccessCacheability() {
+    return (new CacheableMetadata())
+      ->setCacheTags(['4xx-response', 'http_response'])
+      ->setCacheContexts(['user.roles']);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function getExpectedUnauthorizedEntityAccessCacheability($is_authenticated) {
+    // @see \Drupal\block\BlockAccessControlHandler::checkAccess()
+    return parent::getExpectedUnauthorizedEntityAccessCacheability($is_authenticated)
+      ->addCacheTags([
+        'config:block.block.llama',
+        $is_authenticated ? 'user:2' : 'user:0',
+      ]);
+  }
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockXmlAnonTest.php

@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\AnonResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ */
+class BlockXmlAnonTest extends BlockResourceTestBase {
+
+  use AnonResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockXmlBasicAuthTest.php

@@ -0,0 +1,43 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\BasicAuthResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ */
+class BlockXmlBasicAuthTest extends BlockResourceTestBase {
+
+  use BasicAuthResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['basic_auth'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'basic_auth';
+
+}

web/core/modules/block/tests/src/Functional/Rest/BlockXmlCookieTest.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Rest;
+
+use Drupal\Tests\rest\Functional\CookieResourceTestTrait;
+use Drupal\Tests\rest\Functional\EntityResource\XmlEntityNormalizationQuirksTrait;
+
+/**
+ * @group rest
+ */
+class BlockXmlCookieTest extends BlockResourceTestBase {
+
+  use CookieResourceTestTrait;
+  use XmlEntityNormalizationQuirksTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $format = 'xml';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $mimeType = 'text/xml; charset=UTF-8';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $auth = 'cookie';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+}

web/core/modules/block/tests/src/Functional/Update/MenuBlockDepthTest.php

@@ -0,0 +1,42 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Update;
+
+use Drupal\block\Entity\Block;
+use Drupal\FunctionalTests\Update\UpdatePathTestBase;
+
+/**
+ * Tests update path for the `depth` setting of menu blocks.
+ *
+ * @group system
+ */
+final class MenuBlockDepthTest extends UpdatePathTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setDatabaseDumpFiles(): void {
+    $this->databaseDumpFiles = [
+      __DIR__ . '/../../../../../system/tests/fixtures/update/drupal-10.3.0.bare.standard.php.gz',
+      __DIR__ . '/../../../fixtures/update/add-menu-block-with-zero-depth.php',
+    ];
+  }
+
+  /**
+   * Tests that menu blocks with a `depth` setting of 0 are changed to NULL.
+   */
+  public function testUpdate(): void {
+    $settings = Block::load('olivero_account_menu')?->get('settings');
+    $this->assertIsArray($settings);
+    $this->assertSame(0, $settings['depth']);
+
+    $this->runUpdates();
+
+    $settings = Block::load('olivero_account_menu')?->get('settings');
+    $this->assertIsArray($settings);
+    $this->assertNull($settings['depth']);
+  }
+
+}

web/core/modules/block/tests/src/Functional/Views/DisplayBlockTest.php

@@ -0,0 +1,412 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Functional\Views;
+
+use Drupal\Component\Serialization\Json;
+use Drupal\Component\Utility\Crypt;
+use Drupal\Core\Site\Settings;
+use Drupal\Core\Url;
+use Drupal\Tests\block\Functional\AssertBlockAppearsTrait;
+use Drupal\Tests\system\Functional\Cache\AssertPageCacheContextsAndTagsTrait;
+use Drupal\Tests\views\Functional\ViewTestBase;
+use Drupal\views\Entity\View;
+use Drupal\views\Views;
+use Drupal\Core\Template\Attribute;
+
+/**
+ * Tests the block display plugin.
+ *
+ * @group block
+ * @see \Drupal\views\Plugin\views\display\Block
+ */
+class DisplayBlockTest extends ViewTestBase {
+
+  use AssertPageCacheContextsAndTagsTrait;
+  use AssertBlockAppearsTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'node',
+    'block_test_views',
+    'test_page_test',
+    'contextual',
+    'views_ui',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Views used by this test.
+   *
+   * @var array
+   */
+  public static $testViews = ['test_view_block', 'test_view_block2'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp($import_test_views = TRUE, $modules = ['block_test_views']): void {
+    parent::setUp($import_test_views, $modules);
+
+    $this->enableViewsTestModule();
+  }
+
+  /**
+   * Tests default and content block categories.
+   */
+  public function testBlockCategory(): void {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer views',
+      'administer blocks',
+    ]));
+
+    // Create a new view in the UI.
+    $edit = [];
+    $edit['label'] = $this->randomString();
+    $edit['id'] = $this->randomMachineName();
+    $edit['show[wizard_key]'] = 'standard:views_test_data';
+    $edit['description'] = $this->randomString();
+    $edit['block[create]'] = TRUE;
+    $edit['block[style][row_plugin]'] = 'fields';
+    $this->drupalGet('admin/structure/views/add');
+    $this->submitForm($edit, 'Save and edit');
+
+    $pattern = '//tr[.//td[text()=:category] and .//td//a[contains(@href, :href)]]';
+    $arguments = [
+      ':href' => Url::fromRoute('block.admin_add', [
+        'plugin_id' => 'views_block:' . $edit['id'] . '-block_1',
+        'theme' => 'stark',
+      ])->toString(),
+      ':category' => 'Lists (Views)',
+    ];
+
+    // Test that the block was given a default category corresponding to its
+    // base table.
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Place block');
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery($pattern, $arguments));
+
+    // Duplicate the block before changing the category.
+    $this->drupalGet('admin/structure/views/view/' . $edit['id'] . '/edit/block_1');
+    $this->submitForm([], 'Duplicate Block');
+    $this->assertSession()->addressEquals('admin/structure/views/view/' . $edit['id'] . '/edit/block_2');
+
+    // Change the block category to a random string.
+    $this->drupalGet('admin/structure/views/view/' . $edit['id'] . '/edit/block_1');
+    $this->assertSession()->elementTextEquals('named', ['id', 'views-block-1-block-category'], 'Lists (Views)');
+    $this->clickLink('Lists (Views)');
+    $category = $this->randomString();
+    $this->submitForm(['block_category' => $category], 'Apply');
+
+    // Duplicate the block after changing the category.
+    $this->submitForm([], 'Duplicate Block');
+    $this->assertSession()->addressEquals('admin/structure/views/view/' . $edit['id'] . '/edit/block_3');
+
+    $this->submitForm([], 'Save');
+
+    // Test that the blocks are listed under the correct categories.
+    $arguments[':category'] = $category;
+    $this->drupalGet('admin/structure/block');
+    $this->clickLink('Place block');
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery($pattern, $arguments));
+
+    // Test that the first duplicated test block remains in the original
+    // category.
+    $arguments = [
+      ':href' => Url::fromRoute('block.admin_add', [
+        'plugin_id' => 'views_block:' . $edit['id'] . '-block_2',
+        'theme' => 'stark',
+      ])->toString(),
+      ':category' => 'Lists (Views)',
+    ];
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery($pattern, $arguments));
+
+    // Test that the second duplicated test block appears in the custom
+    // category.
+    $arguments = [
+      ':href' => Url::fromRoute('block.admin_add', [
+        'plugin_id' => 'views_block:' . $edit['id'] . '-block_3',
+        'theme' => 'stark',
+      ])->toString(),
+      ':category' => $category,
+    ];
+    $this->assertSession()->elementExists('xpath', $this->assertSession()->buildXPathQuery($pattern, $arguments));
+  }
+
+  /**
+   * Tests removing a block display.
+   */
+  public function testDeleteBlockDisplay(): void {
+    // To test all combinations possible we first place create two instances
+    // of the block display of the first view.
+    $block_1 = $this->drupalPlaceBlock('views_block:test_view_block-block_1', ['label' => 'test_view_block-block_1:1']);
+    $block_2 = $this->drupalPlaceBlock('views_block:test_view_block-block_1', ['label' => 'test_view_block-block_1:2']);
+
+    // Then we add one instance of blocks for each of the two displays of the
+    // second view.
+    $block_3 = $this->drupalPlaceBlock('views_block:test_view_block2-block_1', ['label' => 'test_view_block2-block_1']);
+    $block_4 = $this->drupalPlaceBlock('views_block:test_view_block2-block_2', ['label' => 'test_view_block2-block_2']);
+
+    $this->drupalGet('test-page');
+    $this->assertBlockAppears($block_1);
+    $this->assertBlockAppears($block_2);
+    $this->assertBlockAppears($block_3);
+    $this->assertBlockAppears($block_4);
+
+    $block_storage = $this->container->get('entity_type.manager')->getStorage('block');
+
+    // Remove the block display, so both block entities from the first view
+    // should both disappear.
+    $view = Views::getView('test_view_block');
+    $view->initDisplay();
+    $view->displayHandlers->remove('block_1');
+    $view->storage->save();
+
+    $this->assertNull($block_storage->load($block_1->id()), 'The block for this display was removed.');
+    $this->assertNull($block_storage->load($block_2->id()), 'The block for this display was removed.');
+    $this->assertNotEmpty($block_storage->load($block_3->id()), 'A block from another view was unaffected.');
+    $this->assertNotEmpty($block_storage->load($block_4->id()), 'A block from another view was unaffected.');
+    $this->drupalGet('test-page');
+    $this->assertNoBlockAppears($block_1);
+    $this->assertNoBlockAppears($block_2);
+    $this->assertBlockAppears($block_3);
+    $this->assertBlockAppears($block_4);
+
+    // Remove the first block display of the second view and ensure the block
+    // instance of the second block display still exists.
+    $view = Views::getView('test_view_block2');
+    $view->initDisplay();
+    $view->displayHandlers->remove('block_1');
+    $view->storage->save();
+
+    $this->assertNull($block_storage->load($block_3->id()), 'The block for this display was removed.');
+    $this->assertNotEmpty($block_storage->load($block_4->id()), 'A block from another display on the same view was unaffected.');
+    $this->drupalGet('test-page');
+    $this->assertNoBlockAppears($block_3);
+    $this->assertBlockAppears($block_4);
+  }
+
+  /**
+   * Tests the block form for a Views block.
+   */
+  public function testViewsBlockForm(): void {
+    $this->drupalLogin($this->drupalCreateUser(['administer blocks']));
+    $default_theme = $this->config('system.theme')->get('default');
+    $this->drupalGet('admin/structure/block/add/views_block:test_view_block-block_1/' . $default_theme);
+    $this->assertSession()->fieldNotExists('label');
+    // Test that the machine name field is hidden from display and has been
+    // saved as expected from the default value.
+    $this->assertSession()->fieldNotExists('edit-machine-name', NULL);
+
+    // Save the block.
+    $edit = ['region' => 'content'];
+    $this->submitForm($edit, 'Save block');
+    $storage = $this->container->get('entity_type.manager')->getStorage('block');
+    $block = $storage->load($default_theme . '_views_block__test_view_block_block_1');
+    // This will only return a result if our new block has been created with the
+    // expected machine name.
+    $this->assertNotEmpty($block, 'The expected block was loaded.');
+
+    for ($i = 2; $i <= 3; $i++) {
+      // Place the same block again and make sure we have a new ID.
+      $this->drupalGet('admin/structure/block/add/views_block:test_view_block-block_1/' . $default_theme);
+      $this->submitForm($edit, 'Save block');
+      $block = $storage->load($default_theme . '_views_block__test_view_block_block_1_' . $i);
+      // This will only return a result if our new block has been created with
+      // the expected machine name.
+      $this->assertNotEmpty($block, 'The expected block was loaded.');
+    }
+
+    // Tests the override capability of items per page.
+    $this->drupalGet('admin/structure/block/add/views_block:test_view_block-block_1/' . $default_theme);
+    $edit = ['region' => 'content'];
+    $edit['settings[override][items_per_page]'] = 10;
+
+    $this->drupalGet('admin/structure/block/add/views_block:test_view_block-block_1/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    $block = $storage->load($default_theme . '_views_block__test_view_block_block_1_4');
+    $config = $block->getPlugin()->getConfiguration();
+    $this->assertEquals(10, $config['items_per_page'], "'Items per page' is properly saved.");
+
+    $edit['settings[override][items_per_page]'] = 5;
+    $this->drupalGet('admin/structure/block/manage/' . $default_theme . '_views_block__test_view_block_block_1_4');
+    $this->submitForm($edit, 'Save block');
+
+    $block = $storage->load($default_theme . '_views_block__test_view_block_block_1_4');
+
+    $config = $block->getPlugin()->getConfiguration();
+    $this->assertEquals(5, $config['items_per_page'], "'Items per page' is properly saved.");
+
+    // Tests the override of the label capability.
+    $edit = ['region' => 'content'];
+    $edit['settings[views_label_checkbox]'] = 1;
+    $edit['settings[views_label]'] = 'Custom title';
+    $this->drupalGet('admin/structure/block/add/views_block:test_view_block-block_1/' . $default_theme);
+    $this->submitForm($edit, 'Save block');
+
+    $block = $storage->load($default_theme . '_views_block__test_view_block_block_1_5');
+    $config = $block->getPlugin()->getConfiguration();
+    $this->assertEquals('Custom title', $config['views_label'], "'Label' is properly saved.");
+  }
+
+  /**
+   * Tests the actual rendering of the views block.
+   */
+  public function testBlockRendering(): void {
+    // Create a block and set a custom title.
+    $block = $this->drupalPlaceBlock('views_block:test_view_block-block_1', [
+      'label' => 'test_view_block-block_1:1',
+      'views_label' => 'Custom title',
+      'region' => 'sidebar_first',
+    ]);
+    $block_xpath = $this->assertSession()->buildXPathQuery('//aside[contains(@class, "layout-sidebar-first")]//div[@id = :id]', [
+      ':id' => 'block-' . $block->id(),
+    ]);
+    $this->drupalGet('');
+    $this->assertSession()->elementTextEquals('xpath', "{$block_xpath}/h2", 'Custom title');
+    $this->assertSession()->elementTextEquals('xpath', "{$block_xpath}//footer", 'Custom title');
+
+    // Don't override the title anymore.
+    $plugin = $block->getPlugin();
+    $plugin->setConfigurationValue('views_label', '');
+    $block->save();
+
+    $this->drupalGet('');
+    $this->assertSession()->elementTextEquals('xpath', "{$block_xpath}/h2", 'test_view_block');
+    $this->assertSession()->elementTextEquals('xpath', "{$block_xpath}//footer", 'test_view_block');
+
+    // Hide the title.
+    $block->getPlugin()->setConfigurationValue('label_display', FALSE);
+    $block->save();
+
+    $this->drupalGet('');
+    $this->assertSession()->elementNotExists('xpath', "{$block_xpath}/h2");
+
+    $this->assertCacheTags(array_merge($block->getCacheTags(), ['block_view', 'config:block_list', 'config:system.site', 'config:views.view.test_view_block', 'http_response', 'CACHE_MISS_IF_UNCACHEABLE_HTTP_METHOD:form', 'rendered']));
+  }
+
+  /**
+   * Tests the various test cases of empty block rendering.
+   */
+  public function testBlockEmptyRendering(): void {
+    $url = new Url('test_page_test.test_page');
+    // Remove all views_test_data entries.
+    \Drupal::database()->truncate('views_test_data')->execute();
+    /** @var \Drupal\views\ViewEntityInterface $view */
+    $view = View::load('test_view_block');
+    $view->invalidateCaches();
+
+    $block = $this->drupalPlaceBlock('views_block:test_view_block-block_1', ['label' => 'test_view_block-block_1:1', 'views_label' => 'Custom title']);
+    $block_xpath = $this->assertSession()->buildXPathQuery('//div[@id = :id]', [
+      ':id' => 'block-' . $block->id(),
+    ]);
+    $this->drupalGet('');
+    $this->assertSession()->elementsCount('xpath', $block_xpath, 1);
+
+    $display = &$view->getDisplay('block_1');
+    $display['display_options']['block_hide_empty'] = TRUE;
+    $view->save();
+
+    $this->drupalGet($url);
+    $this->assertSession()->elementNotExists('xpath', $block_xpath);
+    // Ensure that the view cacheability metadata is propagated even, for an
+    // empty block.
+    $this->assertCacheTags(array_merge($block->getCacheTags(), ['block_view', 'config:block_list', 'config:views.view.test_view_block', 'http_response', 'rendered']));
+    $this->assertCacheContexts(['url.query_args:_wrapper_format']);
+
+    // Add a header displayed on empty result.
+    $display = &$view->getDisplay('block_1');
+    $display['display_options']['defaults']['header'] = FALSE;
+    $display['display_options']['header']['example'] = [
+      'field' => 'area_text_custom',
+      'id' => 'area_text_custom',
+      'table' => 'views',
+      'plugin_id' => 'text_custom',
+      'content' => 'test header',
+      'empty' => TRUE,
+    ];
+    $view->save();
+
+    $this->drupalGet($url);
+    $this->assertSession()->elementsCount('xpath', $block_xpath, 1);
+    $this->assertCacheTags(array_merge($block->getCacheTags(), ['block_view', 'config:block_list', 'config:views.view.test_view_block', 'http_response', 'rendered']));
+    $this->assertCacheContexts(['url.query_args:_wrapper_format']);
+
+    // Hide the header on empty results.
+    $display = &$view->getDisplay('block_1');
+    $display['display_options']['defaults']['header'] = FALSE;
+    $display['display_options']['header']['example'] = [
+      'field' => 'area_text_custom',
+      'id' => 'area_text_custom',
+      'table' => 'views',
+      'plugin_id' => 'text_custom',
+      'content' => 'test header',
+      'empty' => FALSE,
+    ];
+    $view->save();
+
+    $this->drupalGet($url);
+    $this->assertSession()->elementNotExists('xpath', $block_xpath);
+    $this->assertCacheTags(array_merge($block->getCacheTags(), ['block_view', 'config:block_list', 'config:views.view.test_view_block', 'http_response', 'rendered']));
+    $this->assertCacheContexts(['url.query_args:_wrapper_format']);
+
+    // Add an empty text.
+    $display = &$view->getDisplay('block_1');
+    $display['display_options']['defaults']['empty'] = FALSE;
+    $display['display_options']['empty']['example'] = [
+      'field' => 'area_text_custom',
+      'id' => 'area_text_custom',
+      'table' => 'views',
+      'plugin_id' => 'text_custom',
+      'content' => 'test empty',
+    ];
+    $view->save();
+
+    $this->drupalGet($url);
+    $this->assertSession()->elementsCount('xpath', $block_xpath, 1);
+    $this->assertCacheTags(array_merge($block->getCacheTags(), ['block_view', 'config:block_list', 'config:views.view.test_view_block', 'http_response', 'rendered']));
+    $this->assertCacheContexts(['url.query_args:_wrapper_format']);
+  }
+
+  /**
+   * Tests the contextual links on a Views block.
+   */
+  public function testBlockContextualLinks(): void {
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer views',
+      'access contextual links',
+      'administer blocks',
+    ]));
+    $block = $this->drupalPlaceBlock('views_block:test_view_block-block_1');
+    $cached_block = $this->drupalPlaceBlock('views_block:test_view_block-block_1');
+    $this->drupalGet('test-page');
+
+    $id = 'block:block=' . $block->id() . ':langcode=en|entity.view.edit_form:view=test_view_block:location=block&name=test_view_block&display_id=block_1&langcode=en';
+    $id_token = Crypt::hmacBase64($id, Settings::getHashSalt() . $this->container->get('private_key')->get());
+    $cached_id = 'block:block=' . $cached_block->id() . ':langcode=en|entity.view.edit_form:view=test_view_block:location=block&name=test_view_block&display_id=block_1&langcode=en';
+    $cached_id_token = Crypt::hmacBase64($cached_id, Settings::getHashSalt() . $this->container->get('private_key')->get());
+    // @see \Drupal\contextual\Tests\ContextualDynamicContextTest:assertContextualLinkPlaceHolder()
+    // Check existence of the contextual link placeholders.
+    $this->assertSession()->responseContains('<div' . new Attribute(['data-contextual-id' => $id, 'data-contextual-token' => $id_token, 'data-drupal-ajax-container' => '']) . '></div>');
+    $this->assertSession()->responseContains('<div' . new Attribute(['data-contextual-id' => $cached_id, 'data-contextual-token' => $cached_id_token, 'data-drupal-ajax-container' => '']) . '></div>');
+
+    // Get server-rendered contextual links.
+    // @see \Drupal\contextual\Tests\ContextualDynamicContextTest:renderContextualLinks()
+    $post = ['ids[0]' => $id, 'ids[1]' => $cached_id, 'tokens[0]' => $id_token, 'tokens[1]' => $cached_id_token];
+    $url = 'contextual/render?_format=json,destination=test-page';
+    $this->getSession()->getDriver()->getClient()->request('POST', $url, $post);
+    $this->assertSession()->statusCodeEquals(200);
+    $json = Json::decode($this->getSession()->getPage()->getContent());
+    $this->assertSame('<ul class="contextual-links"><li><a href="' . base_path() . 'admin/structure/block/manage/' . $block->id() . '">Configure block</a></li><li><a href="' . base_path() . 'admin/structure/block/manage/' . $block->id() . '/delete">Remove block</a></li><li><a href="' . base_path() . 'admin/structure/views/view/test_view_block/edit/block_1">Edit view</a></li></ul>', $json[$id]);
+    $this->assertSame('<ul class="contextual-links"><li><a href="' . base_path() . 'admin/structure/block/manage/' . $cached_block->id() . '">Configure block</a></li><li><a href="' . base_path() . 'admin/structure/block/manage/' . $cached_block->id() . '/delete">Remove block</a></li><li><a href="' . base_path() . 'admin/structure/views/view/test_view_block/edit/block_1">Edit view</a></li></ul>', $json[$cached_id]);
+  }
+
+}

web/core/modules/block/tests/src/FunctionalJavascript/BlockAddTest.php

@@ -0,0 +1,63 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\FunctionalJavascript;
+
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests the JS functionality in the block add form.
+ *
+ * @group block
+ */
+class BlockAddTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'user',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Tests the AJAX for the theme selector.
+   */
+  public function testBlockAddThemeSelector(): void {
+    \Drupal::service('theme_installer')->install(['claro']);
+
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+    ]));
+
+    $this->drupalGet('admin/structure/block/add/system_powered_by_block');
+    $assert_session = $this->assertSession();
+    // Pick a theme with a region that does not exist in another theme.
+    $assert_session->selectExists('Theme')->selectOption('claro');
+    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->selectExists('Region')->selectOption('pre_content');
+    // Switch to a theme that doesn't contain the region selected above.
+    $assert_session->selectExists('Theme')->selectOption('stark');
+    $assert_session->assertWaitOnAjaxRequest();
+    $assert_session->pageTextNotContains('The submitted value Pre-content in the Region element is not allowed.');
+    $assert_session->optionExists('Region', '- Select -');
+    // Check that the summary line is not present in the title.
+    $summary_text = $this->getSession()->getPage()->find('css', 'li.vertical-tabs__menu-item:nth-child(1) > a:nth-child(1) > span:nth-child(2)')->getText();
+    $assert_session->elementTextContains('css', '.vertical-tabs__menu-item-title', 'Response status');
+    $assert_session->elementTextNotContains('css', '.vertical-tabs__menu-item-title', $summary_text);
+
+    // Search for the "Pages" tab link and click it
+    $this->getSession()->getPage()->find('css', 'a[href="#edit-visibility-request-path"]')->click();
+    // Check that the corresponding form section is open and visible.
+    $form_section = $this->getSession()->getPage()->find('css', '#edit-visibility-request-path');
+    $this->assertNotEmpty($form_section, 'The "Pages" form section exists.');
+    $this->assertTrue($form_section->isVisible(), 'The "Pages" form section is visible after clicking the tab.');
+  }
+
+}

web/core/modules/block/tests/src/FunctionalJavascript/BlockContextualLinksTest.php

@@ -0,0 +1,67 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\FunctionalJavascript;
+
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests the contextual links added while rendering the block.
+ *
+ * @group block
+ */
+class BlockContextualLinksTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['user', 'block', 'contextual'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * Block id of the block.
+   *
+   * @var string
+   */
+  protected $blockId;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->drupalLogin($this->drupalCreateUser([
+      'administer blocks',
+      'access administration pages',
+      'access contextual links',
+    ]));
+    $this->blockId = $this->defaultTheme . '_powered';
+    $this->placeBlock('system_powered_by_block', [
+      'id' => $this->blockId,
+      'region' => 'content',
+    ]);
+  }
+
+  /**
+   * Test that remove/configure contextual links are present in the block.
+   */
+  public function testBlockContextualRemoveLinks(): void {
+    $this->drupalGet('<front>');
+    $contextual_id = "[data-contextual-id^='block:block=$this->blockId:langcode=en']";
+    $this->assertSession()->waitForElement('css', "$contextual_id .contextual-links");
+
+    $expected_configure_block_link = base_path() . 'admin/structure/block/manage/' . $this->blockId;
+    $actual_configure_block_link = parse_url($this->getSession()->getPage()->findLink('Configure block')->getAttribute('href'));
+    $this->assertEquals($expected_configure_block_link, $actual_configure_block_link['path']);
+
+    $expected_remove_block_link = base_path() . 'admin/structure/block/manage/' . $this->blockId . '/delete';
+    $actual_remove_block_link = parse_url($this->getSession()->getPage()->findLink('Remove block')->getAttribute('href'));
+    $this->assertEquals($expected_remove_block_link, $actual_remove_block_link['path']);
+  }
+
+}

web/core/modules/block/tests/src/FunctionalJavascript/BlockDragTest.php

@@ -0,0 +1,96 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\FunctionalJavascript;
+
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests drag and drop blocks on block layout page.
+ *
+ * @group block
+ */
+class BlockDragTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['user', 'block', 'node'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'olivero';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+    ]);
+    $this->drupalLogin($admin_user);
+  }
+
+  /**
+   * Tests drag and drop blocks.
+   */
+  public function testDragAndDropBlocks(): void {
+    // Resize window to work around https://github.com/bitovi/syn/issues/164.
+    $this->getSession()->resizeWindow(1024, 2048);
+    $this->drupalGet('admin/structure/block');
+    $assertSession = $this->assertSession();
+    $session = $this->getSession();
+    $page = $session->getPage();
+
+    // Test if drag orientation on block layout page was applied with success.
+    $this->assertNotEmpty($assertSession->waitForElementVisible('css', '.tabledrag-handle-y'));
+
+    // Dragging main-menu and status messages to header region.
+    $siteBranding = $this->getDragRow($page, 'edit-blocks-olivero-site-branding');
+    $mainMenuRow = $this->getDragRow($page, 'edit-blocks-olivero-main-menu');
+    $mainMenuRow->dragTo($siteBranding);
+    $messages = $this->getDragRow($page, 'edit-blocks-olivero-messages');
+    $messages->dragTo($siteBranding);
+
+    // Test if both blocks above was positioned on the header region.
+    $this->assertEquals(
+      'header',
+      $page->findField('edit-blocks-olivero-main-menu-region')->getValue(),
+      'Main menu should be positioned on header region'
+    );
+    $this->assertEquals(
+      'header',
+      $page->findField('edit-blocks-olivero-messages-region')->getValue(),
+      'Status messages should be positioned on header region'
+    );
+
+    // Check if the message unsaved changed appears.
+    $assertSession->pageTextContains('You have unsaved changes.');
+
+    // Test if the message for empty regions appear after drag the unique block
+    // on the region.
+    $noBlockMessage = $page->find('css', 'tr[data-drupal-selector="edit-blocks-region-primary-menu-message"] td')->getText();
+    $this->assertSession()->assert($noBlockMessage === 'No blocks in this region', 'Region primary menu should be empty.');
+
+    // Testing drag row to an empty region.
+    $pageTitle = $this->getDragRow($page, 'edit-blocks-olivero-page-title');
+    $heroRegion = $page->find('css', 'tr[data-drupal-selector="edit-blocks-region-hero-message"]');
+    $pageTitle->dragTo($heroRegion);
+    $this->assertSession()->assert(
+      $page->find('css', 'tr[data-drupal-selector="edit-blocks-region-hero-message"] td')->getText() !== 'No blocks in this region',
+      "Region here shouldn't be empty"
+    );
+
+  }
+
+  /**
+   * Helper function to find block tr element on the page.
+   */
+  private function getDragRow($page, $blockId) {
+    return $page->find('css', '#blocks tbody tr[data-drupal-selector="' . $blockId . '"] a.tabledrag-handle');
+  }
+
+}

web/core/modules/block/tests/src/FunctionalJavascript/BlockFilterTest.php

@@ -0,0 +1,114 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\FunctionalJavascript;
+
+use Behat\Mink\Element\NodeElement;
+use Drupal\FunctionalJavascriptTests\WebDriverTestBase;
+
+/**
+ * Tests the JavaScript functionality of the block add filter.
+ *
+ * @group block
+ */
+class BlockFilterTest extends WebDriverTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['user', 'block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected $defaultTheme = 'stark';
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $admin_user = $this->drupalCreateUser([
+      'administer blocks',
+    ]);
+
+    $this->drupalLogin($admin_user);
+  }
+
+  /**
+   * Tests block filter.
+   */
+  public function testBlockFilter(): void {
+    $this->drupalGet('admin/structure/block');
+    $assertSession = $this->assertSession();
+    $session = $this->getSession();
+    $page = $session->getPage();
+
+    // Find the block filter field on the add-block dialog.
+    $page->find('css', '#edit-blocks-region-header-title')->click();
+    $filter = $assertSession->waitForElement('css', '.block-filter-text');
+
+    // Get all block rows, for assertions later.
+    $block_rows = $page->findAll('css', '.block-add-table tbody tr');
+
+    // Test block filter reduces the number of visible rows.
+    $filter->setValue('ad');
+    $session->wait(10000, 'jQuery("#drupal-live-announce").html().indexOf("blocks are available") > -1');
+    $visible_rows = $this->filterVisibleElements($block_rows);
+    if (count($block_rows) > 0) {
+      $this->assertNotSameSize($block_rows, $visible_rows);
+    }
+
+    // Test Drupal.announce() message when multiple matches are expected.
+    $expected_message = count($visible_rows) . ' blocks are available in the modified list.';
+    $this->assertAnnounceContains($expected_message);
+
+    // Test Drupal.announce() message when only one match is expected.
+    $filter->setValue('Powered by');
+    $session->wait(10000, 'jQuery("#drupal-live-announce").html().indexOf("block is available") > -1');
+    $visible_rows = $this->filterVisibleElements($block_rows);
+    $this->assertCount(1, $visible_rows);
+    $expected_message = '1 block is available in the modified list.';
+    $this->assertAnnounceContains($expected_message);
+
+    // Test Drupal.announce() message when no matches are expected.
+    $filter->setValue('Pan-Galactic Gargle Blaster');
+    $session->wait(10000, 'jQuery("#drupal-live-announce").html().indexOf("0 blocks are available") > -1');
+    $visible_rows = $this->filterVisibleElements($block_rows);
+    $this->assertCount(0, $visible_rows);
+    $expected_message = '0 blocks are available in the modified list.';
+    $this->assertAnnounceContains($expected_message);
+  }
+
+  /**
+   * Removes any non-visible elements from the passed array.
+   *
+   * @param \Behat\Mink\Element\NodeElement[] $elements
+   *   An array of node elements.
+   *
+   * @return \Behat\Mink\Element\NodeElement[]
+   *   An array of visible elements.
+   */
+  protected function filterVisibleElements(array $elements): array {
+    $elements = array_filter($elements, function (NodeElement $element) {
+      return $element->isVisible();
+    });
+    return $elements;
+  }
+
+  /**
+   * Checks for inclusion of text in #drupal-live-announce.
+   *
+   * @param string $expected_message
+   *   The text expected to be present in #drupal-live-announce.
+   *
+   * @internal
+   */
+  protected function assertAnnounceContains(string $expected_message): void {
+    $assert_session = $this->assertSession();
+    $this->assertNotEmpty($assert_session->waitForElement('css', "#drupal-live-announce:contains('$expected_message')"));
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockConfigSchemaTest.php

@@ -0,0 +1,95 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\Tests\SchemaCheckTestTrait;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests the block config schema.
+ *
+ * @group block
+ */
+class BlockConfigSchemaTest extends KernelTestBase {
+
+  use SchemaCheckTestTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'block_content',
+    'comment',
+    'node',
+    // \Drupal\block\Entity\Block->preSave() calls system_region_list().
+    'system',
+    'taxonomy',
+    'user',
+    'text',
+  ];
+
+  /**
+   * The typed config manager.
+   *
+   * @var \Drupal\Core\Config\TypedConfigManagerInterface
+   */
+  protected $typedConfig;
+
+  /**
+   * The block manager.
+   *
+   * @var \Drupal\Core\Block\BlockManagerInterface
+   */
+  protected $blockManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->typedConfig = \Drupal::service('config.typed');
+    $this->blockManager = \Drupal::service('plugin.manager.block');
+    $this->installEntitySchema('block_content');
+    $this->installEntitySchema('taxonomy_term');
+    $this->installEntitySchema('node');
+    $this->container->get('theme_installer')->install(['stark']);
+  }
+
+  /**
+   * Tests the block config schema for block plugins.
+   */
+  public function testBlockConfigSchema(): void {
+    foreach ($this->blockManager->getDefinitions() as $block_id => $definition) {
+      // Skip the syndicate block as it is deprecated.
+      if ($block_id === 'node_syndicate_block') {
+        continue;
+      }
+      $id = $this->randomMachineName();
+      $block = Block::create([
+        'id' => $id,
+        'theme' => 'stark',
+        'weight' => 00,
+        'status' => TRUE,
+        'region' => 'content',
+        'plugin' => $block_id,
+        'settings' => [
+          'label' => $this->randomMachineName(),
+          'provider' => 'system',
+          'label_display' => FALSE,
+        ],
+        'visibility' => [],
+      ]);
+      $block->save();
+
+      $config = $this->config("block.block.$id");
+      $this->assertEquals($id, $config->get('id'));
+      $this->assertConfigSchema($this->typedConfig, $config->getName(), $config->get());
+    }
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockConfigSyncTest.php

@@ -0,0 +1,86 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\Core\Config\ConfigInstallerInterface;
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Extension\ThemeInstallerInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests that blocks are not created during config sync.
+ *
+ * @group block
+ */
+class BlockConfigSyncTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'system'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    \Drupal::service(ThemeInstallerInterface::class)
+      ->install(['stark', 'claro']);
+
+    // Delete all existing blocks.
+    foreach (Block::loadMultiple() as $block) {
+      $block->delete();
+    }
+
+    // Set the default theme.
+    $this->config('system.theme')
+      ->set('default', 'stark')
+      ->save();
+
+    // Create a block for the default theme to be copied later.
+    Block::create([
+      'id' => 'test_block',
+      'plugin' => 'system_powered_by_block',
+      'region' => 'content',
+      'theme' => 'stark',
+    ])->save();
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function register(ContainerBuilder $container): void {
+    parent::register($container);
+    $container->setParameter('install_profile', 'testing');
+  }
+
+  /**
+   * Tests blocks are not created during config sync.
+   *
+   * @param bool $syncing
+   *   Whether or not config is syncing when the hook is invoked.
+   * @param string|null $expected_block_id
+   *   The expected ID of the block that should be created, or NULL if no block
+   *   should be created.
+   *
+   * @testWith [true, null]
+   *   [false, "claro_test_block"]
+   */
+  public function testNoBlocksCreatedDuringConfigSync(bool $syncing, ?string $expected_block_id): void {
+    \Drupal::service(ConfigInstallerInterface::class)
+      ->setSyncing($syncing);
+
+    // Invoke the hook that should skip block creation due to config sync.
+    \Drupal::moduleHandler()->invoke('block', 'themes_installed', [['claro']]);
+    // This should hold true if the "current" install profile triggers an
+    // invocation of hook_modules_installed().
+    \Drupal::moduleHandler()->invoke('block', 'modules_installed', [['testing'], $syncing]);
+
+    $this->assertSame($expected_block_id, Block::load('claro_test_block')?->id());
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockInterfaceTest.php

@@ -0,0 +1,110 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Form\FormState;
+use Drupal\KernelTests\KernelTestBase;
+
+// cspell:ignore displaymessage
+
+/**
+ * Tests that the block plugin can work properly without a supporting entity.
+ *
+ * @group block
+ */
+class BlockInterfaceTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['system', 'block', 'block_test', 'user'];
+
+  /**
+   * Tests configuration and subsequent form() and build() method calls.
+   *
+   * This test is attempting to test the existing block plugin api and all
+   * functionality that is expected to remain consistent. The arrays that are
+   * used for comparison can change, but only to include elements that are
+   * contained within BlockBase or the plugin being tested. Likely these
+   * comparison arrays should get smaller, not larger, as more form/build
+   * elements are moved into a more suitably responsible class.
+   *
+   * Instantiation of the plugin is the primary element being tested here. The
+   * subsequent method calls are just attempting to cause a failure if a
+   * dependency outside of the plugin configuration is required.
+   */
+  public function testBlockInterface(): void {
+    $manager = $this->container->get('plugin.manager.block');
+    $configuration = [
+      'label' => 'Custom Display Message',
+    ];
+    $expected_configuration = [
+      'id' => 'test_block_instantiation',
+      'label' => 'Custom Display Message',
+      'label_display' => BlockPluginInterface::BLOCK_LABEL_VISIBLE,
+      'provider' => 'block_test',
+      'display_message' => 'no message set',
+    ];
+    // Initial configuration of the block at construction time.
+    /** @var \Drupal\Core\Block\BlockPluginInterface $display_block */
+    $display_block = $manager->createInstance('test_block_instantiation', $configuration);
+    $this->assertSame($expected_configuration, $display_block->getConfiguration(), 'The block was configured correctly.');
+
+    // Updating an element of the configuration.
+    $display_block->setConfigurationValue('display_message', 'My custom display message.');
+    $expected_configuration['display_message'] = 'My custom display message.';
+    $this->assertSame($expected_configuration, $display_block->getConfiguration(), 'The block configuration was updated correctly.');
+    $definition = $display_block->getPluginDefinition();
+
+    $expected_form = [
+      'provider' => [
+        '#type' => 'value',
+        '#value' => 'block_test',
+      ],
+      'admin_label' => [
+        '#type' => 'item',
+        '#title' => 'Block description',
+        '#plain_text' => $definition['admin_label'],
+      ],
+      'label' => [
+        '#type' => 'textfield',
+        '#title' => 'Title',
+        '#maxlength' => 255,
+        '#default_value' => 'Custom Display Message',
+        '#required' => TRUE,
+      ],
+      'label_display' => [
+        '#type' => 'checkbox',
+        '#title' => 'Display title',
+        '#default_value' => TRUE,
+        '#return_value' => 'visible',
+      ],
+      'context_mapping' => [],
+      'display_message' => [
+        '#type' => 'textfield',
+        '#title' => 'Display message',
+        '#default_value' => 'My custom display message.',
+      ],
+    ];
+    $form_state = new FormState();
+    // Ensure there are no form elements that do not belong to the plugin.
+    $actual_form = $display_block->buildConfigurationForm([], $form_state);
+    // Remove the visibility sections, as that just tests condition plugins.
+    unset($actual_form['visibility'], $actual_form['visibility_tabs']);
+    $this->assertEquals($expected_form, $actual_form, 'Only the expected form elements were present.');
+
+    $expected_build = [
+      '#children' => 'My custom display message.',
+    ];
+    // Ensure the build array is proper.
+    $this->assertSame($expected_build, $display_block->build(), 'The plugin returned the appropriate build array.');
+
+    // Ensure the machine name suggestion is correct. In truth, this is actually
+    // testing BlockBase's implementation, not the interface itself.
+    $this->assertSame('displaymessage', $display_block->getMachineNameSuggestion(), 'The plugin returned the expected machine name suggestion.');
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockRebuildTest.php

@@ -0,0 +1,123 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\Core\StringTranslation\TranslatableMarkup;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\Tests\block\Traits\BlockCreationTrait;
+use Drupal\block\Hook\BlockHooks;
+
+/**
+ * Tests block_rebuild().
+ *
+ * @group block
+ */
+class BlockRebuildTest extends KernelTestBase {
+
+  use BlockCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'system'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $configSchemaCheckerExclusions = [
+    // These blocks are intentionally put into invalid regions, so they will
+    // violate config schema.
+    // @see ::testRebuildInvalidBlocks()
+    'block.block.invalid_block1',
+    'block.block.invalid_block2',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->container->get('theme_installer')->install(['stark']);
+    $this->container->get('config.factory')->getEditable('system.theme')->set('default', 'stark')->save();
+  }
+
+  /**
+   * @covers \Drupal\block\Hook\BlockHooks::rebuild
+   */
+  public function testRebuildNoBlocks(): void {
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+    $messages = \Drupal::messenger()->all();
+    \Drupal::messenger()->deleteAll();
+    $this->assertEquals([], $messages);
+  }
+
+  /**
+   * @covers \Drupal\block\Hook\BlockHooks::rebuild
+   */
+  public function testRebuildNoInvalidBlocks(): void {
+    $this->placeBlock('system_powered_by_block', ['region' => 'content']);
+
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+    $messages = \Drupal::messenger()->all();
+    \Drupal::messenger()->deleteAll();
+    $this->assertEquals([], $messages);
+  }
+
+  /**
+   * @covers \Drupal\block\Hook\BlockHooks::rebuild
+   */
+  public function testRebuildInvalidBlocks(): void {
+    $this->placeBlock('system_powered_by_block', ['region' => 'content']);
+    $block1 = $this->placeBlock('system_powered_by_block', [
+      'id' => 'invalid_block1',
+    ]);
+    $block2 = $this->placeBlock('system_powered_by_block', [
+      'id' => 'invalid_block2',
+    ]);
+    $block2->disable()->save();
+    // Use the config API directly to bypass Block::preSave().
+    \Drupal::configFactory()->getEditable('block.block.' . $block1->id())->set('region', 'INVALID')->save();
+    \Drupal::configFactory()->getEditable('block.block.' . $block2->id())->set('region', 'INVALID')->save();
+
+    // Reload block entities.
+    $block1 = Block::load($block1->id());
+    $block2 = Block::load($block2->id());
+
+    $this->assertSame('INVALID', $block1->getRegion());
+    $this->assertTrue($block1->status());
+    $this->assertSame('INVALID', $block2->getRegion());
+    $this->assertFalse($block2->status());
+
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+
+    // Reload block entities.
+    $block1 = Block::load($block1->id());
+    $block2 = Block::load($block2->id());
+
+    $messages = \Drupal::messenger()->all();
+    \Drupal::messenger()->deleteAll();
+    $expected = [
+      'warning' => [
+        new TranslatableMarkup('The block %info was assigned to the invalid region %region and has been disabled.', [
+          '%info' => $block1->id(),
+          '%region' => 'INVALID',
+        ]),
+      ],
+    ];
+    $this->assertEquals($expected, $messages);
+
+    $default_region = system_default_region('stark');
+    $this->assertSame($default_region, $block1->getRegion());
+    $this->assertFalse($block1->status());
+    $this->assertSame($default_region, $block2->getRegion());
+    $this->assertFalse($block2->status());
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockStorageUnitTest.php

@@ -0,0 +1,161 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\Core\Config\Entity\ConfigEntityStorage;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\block_test\Plugin\Block\TestHtmlBlock;
+use Drupal\Component\Plugin\Exception\PluginException;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests the storage of blocks.
+ *
+ * @group block
+ */
+class BlockStorageUnitTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'system'];
+
+  /**
+   * The block storage.
+   *
+   * @var \Drupal\Core\Config\Entity\ConfigEntityStorageInterface
+   */
+  protected $controller;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->controller = $this->container->get('entity_type.manager')->getStorage('block');
+
+    $this->container->get('theme_installer')->install(['stark']);
+  }
+
+  /**
+   * Tests CRUD operations.
+   */
+  public function testBlockCRUD(): void {
+    $this->assertInstanceOf(ConfigEntityStorage::class, $this->controller);
+
+    // Run each test method in the same installation.
+    $this->createTests();
+    $this->loadTests();
+    $this->deleteTests();
+  }
+
+  /**
+   * Tests the creation of blocks.
+   */
+  protected function createTests(): void {
+    // Attempt to create a block without a plugin.
+    try {
+      $entity = $this->controller->create([]);
+      $entity->getPlugin();
+      $this->fail('A block without a plugin was created with no exception thrown.');
+    }
+    catch (PluginException $e) {
+      $this->assertEquals('The block \'\' did not specify a plugin.', $e->getMessage(), 'An exception was thrown when a block was created without a plugin.');
+    }
+
+    // Create a block with only required values.
+    $entity = $this->controller->create([
+      'id' => 'test_block',
+      'theme' => 'stark',
+      'region' => 'content',
+      'plugin' => 'test_html',
+    ]);
+    $entity->save();
+
+    $this->assertInstanceOf(Block::class, $entity);
+
+    // Verify all of the block properties.
+    $actual_properties = $this->config('block.block.test_block')->get();
+    $this->assertNotEmpty($actual_properties['uuid'], 'The block UUID is set.');
+    unset($actual_properties['uuid']);
+
+    // Ensure that default values are filled in.
+    $expected_properties = [
+      'langcode' => \Drupal::languageManager()->getDefaultLanguage()->getId(),
+      'status' => TRUE,
+      'dependencies' => ['module' => ['block_test'], 'theme' => ['stark']],
+      'id' => 'test_block',
+      'theme' => 'stark',
+      'region' => 'content',
+      'weight' => 0,
+      'provider' => NULL,
+      'plugin' => 'test_html',
+      'settings' => [
+        'id' => 'test_html',
+        'label' => '',
+        'label_display' => BlockPluginInterface::BLOCK_LABEL_VISIBLE,
+        'provider' => 'block_test',
+      ],
+      'visibility' => [],
+    ];
+
+    $this->assertSame($expected_properties, $actual_properties);
+
+    $this->assertInstanceOf(TestHtmlBlock::class, $entity->getPlugin());
+  }
+
+  /**
+   * Tests the loading of blocks.
+   */
+  protected function loadTests(): void {
+    $entity = $this->controller->load('test_block');
+
+    $this->assertInstanceOf(Block::class, $entity);
+
+    // Verify several properties of the block.
+    $this->assertSame('content', $entity->getRegion());
+    $this->assertTrue($entity->status());
+    $this->assertEquals('stark', $entity->getTheme());
+    $this->assertNotEmpty($entity->uuid());
+  }
+
+  /**
+   * Tests the deleting of blocks.
+   */
+  protected function deleteTests(): void {
+    $entity = $this->controller->load('test_block');
+
+    // Ensure that the storage isn't currently empty.
+    $config_storage = $this->container->get('config.storage');
+    $config = $config_storage->listAll('block.block.');
+    $this->assertNotEmpty($config, 'There are blocks in config storage.');
+
+    // Delete the block.
+    $entity->delete();
+
+    // Ensure that the storage is now empty.
+    $config = $config_storage->listAll('block.block.');
+    $this->assertEmpty($config, 'There are no blocks in config storage.');
+  }
+
+  /**
+   * Tests the installation of default blocks.
+   */
+  public function testDefaultBlocks(): void {
+    \Drupal::service('theme_installer')->install(['stark']);
+    $entities = $this->controller->loadMultiple();
+    $this->assertEmpty($entities, 'There are no blocks initially.');
+
+    // Install the block_test.module, so that its default config is installed.
+    $this->installConfig(['block_test']);
+
+    $entities = $this->controller->loadMultiple();
+    $entity = reset($entities);
+    $this->assertEquals('test_block', $entity->id(), 'The default test block was loaded.');
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockTemplateSuggestionsTest.php

@@ -0,0 +1,56 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\KernelTests\KernelTestBase;
+
+/**
+ * Tests the block_theme_suggestions_block() function.
+ *
+ * @group block
+ */
+class BlockTemplateSuggestionsTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'system',
+  ];
+
+  /**
+   * Tests template suggestions from block_theme_suggestions_block().
+   */
+  public function testBlockThemeHookSuggestions(): void {
+    $this->installConfig(['system']);
+
+    // Create a block using a plugin with derivative to be preprocessed.
+    $block = Block::create([
+      'plugin' => 'system_menu_block:admin',
+      'region' => 'footer',
+      'id' => 'machine_name',
+    ]);
+
+    $variables = [];
+    /** @var \Drupal\Core\Block\BlockPluginInterface $plugin */
+    $plugin = $block->getPlugin();
+    $variables['elements']['#configuration'] = $plugin->getConfiguration();
+    $variables['elements']['#plugin_id'] = $plugin->getPluginId();
+    $variables['elements']['#id'] = $block->id();
+    $variables['elements']['#base_plugin_id'] = $plugin->getBaseId();
+    $variables['elements']['#derivative_plugin_id'] = $plugin->getDerivativeId();
+    $variables['elements']['content'] = [];
+    $suggestions = block_theme_suggestions_block($variables);
+    $this->assertSame([
+      'block__system',
+      'block__system_menu_block',
+      'block__system_menu_block__admin',
+      'block__machine_name',
+    ], $suggestions);
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockValidationTest.php

@@ -0,0 +1,271 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\Core\Config\Entity\ConfigEntityInterface;
+use Drupal\KernelTests\Core\Config\ConfigEntityValidationTestBase;
+
+/**
+ * Tests validation of block entities.
+ *
+ * @group block
+ * @group #slow
+ */
+class BlockValidationTest extends ConfigEntityValidationTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static array $propertiesWithRequiredKeys = [
+    'settings' => [
+      "'id' is a required key.",
+      "'label' is a required key.",
+      "'label_display' is a required key.",
+      "'provider' is a required key.",
+    ],
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static array $propertiesWithOptionalValues = [
+    'provider',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->container->get('theme_installer')->install(['stark']);
+
+    $this->entity = Block::create([
+      'id' => 'test_block',
+      'theme' => 'stark',
+      'plugin' => 'system_powered_by_block',
+      'settings' => [
+        'label' => 'Powered by Drupal 🚀',
+      ],
+    ]);
+    $this->entity->save();
+  }
+
+  /**
+   * Tests validating a block with an unknown plugin ID.
+   */
+  public function testInvalidPluginId(): void {
+    $this->entity->set('plugin', 'block_content:d7c9d8ba-663f-41b4-8756-86bc55c44653');
+    // Block config entities with invalid block plugin IDs automatically fall
+    // back to the `broken` block plugin.
+    // @see https://www.drupal.org/node/2249303
+    // @see \Drupal\Core\Block\BlockManager::getFallbackPluginId()
+    // @see \Drupal\Core\Block\Plugin\Block\Broken
+    $this->assertValidationErrors([]);
+
+    $this->entity->set('plugin', 'non_existent');
+    // @todo Expect error for this in https://www.drupal.org/project/drupal/issues/3377709
+    $this->assertValidationErrors([]);
+  }
+
+  /**
+   * Block names are atypical in that they allow periods in the machine name.
+   */
+  public static function providerInvalidMachineNameCharacters(): array {
+    $cases = parent::providerInvalidMachineNameCharacters();
+    // Remove the existing test case that verifies a machine name containing
+    // periods is invalid.
+    self::assertSame(['period.separated', FALSE], $cases['INVALID: period separated']);
+    unset($cases['INVALID: period separated']);
+    // And instead add a test case that verifies it is allowed for blocks.
+    $cases['VALID: period separated'] = ['period.separated', TRUE];
+    return $cases;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static function setLabel(ConfigEntityInterface $block, string $label): void {
+    static::assertInstanceOf(Block::class, $block);
+    $settings = $block->get('settings');
+    static::assertNotEmpty($settings['label']);
+    $settings['label'] = $label;
+    $block->set('settings', $settings);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testLabelValidation(): void {
+    static::setLabel($this->entity, "Multi\nLine");
+    // TRICKY: because the Block config entity type does not specify a `label`
+    // key, it is impossible for the generic ::testLabelValidation()
+    // implementation in the base class to know at which property to expect a
+    // validation error. Hence it is hardcoded in this case.
+    $this->assertValidationErrors(['settings.label' => "Labels are not allowed to span multiple lines or contain control characters."]);
+  }
+
+  /**
+   * Tests validating a block with a non-existent theme.
+   */
+  public function testThemeValidation(): void {
+    $this->entity->set('theme', 'non_existent');
+    $this->assertValidationErrors([
+      'region' => 'This is not a valid region of the <em class="placeholder">non_existent</em> theme.',
+      'theme' => "Theme 'non_existent' is not installed.",
+    ]);
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function testRequiredPropertyValuesMissing(?array $additional_expected_validation_errors_when_missing = NULL): void {
+    parent::testRequiredPropertyValuesMissing([
+      'region' => [
+        'region' => [
+          'This is not a valid region of the <em class="placeholder">stark</em> theme.',
+          'This value should not be null.',
+        ],
+      ],
+      'theme' => [
+        'region' => 'This block does not say which theme it appears in.',
+      ],
+    ]);
+  }
+
+  /**
+   * Tests validating a block's region in a theme.
+   */
+  public function testRegionValidation(): void {
+    $this->entity->set('region', 'non_existent');
+    $this->assertValidationErrors([
+      'region' => 'This is not a valid region of the <em class="placeholder">stark</em> theme.',
+    ]);
+    // Set a valid region and assert it is saved properly.
+    $this->entity->set('region', 'header');
+    $this->assertValidationErrors([]);
+  }
+
+  /**
+   * Tests validating weight.
+   */
+  public function testWeightValidation(): void {
+    $this->entity->set('weight', $this->randomString());
+    $this->assertValidationErrors([
+      'weight' => [
+        'This value should be a valid number.',
+        'This value should be of the correct primitive type.',
+      ],
+    ]);
+
+    $this->entity->set('weight', 10);
+    $this->assertValidationErrors([]);
+  }
+
+  /**
+   * @group legacy
+   */
+  public function testWeightCannotBeNull(): void {
+    $this->entity->set('weight', NULL);
+    $this->assertNull($this->entity->getWeight());
+    $this->expectDeprecation('Saving a block with a non-integer weight is deprecated in drupal:11.1.0 and removed in drupal:12.0.0. See https://www.drupal.org/node/3462474');
+    $this->entity->save();
+  }
+
+  /**
+   * Data provider for ::testMenuBlockLevelAndDepth().
+   */
+  public static function providerMenuBlockLevelAndDepth(): iterable {
+    yield 'OK: entire tree from first level' => [0, NULL, []];
+
+    yield 'OK: entire tree from third level' => [2, NULL, []];
+
+    yield 'OK: first three levels' => [0, 3, []];
+
+    yield 'INVALID: level is less than 0' => [
+      -2,
+      NULL,
+      [
+        'settings.level' => 'This value should be between <em class="placeholder">0</em> and <em class="placeholder">9</em>.',
+      ],
+    ];
+
+    yield 'INVALID: level is greater than 9' => [
+      11,
+      NULL,
+      [
+        'settings.level' => 'This value should be between <em class="placeholder">0</em> and <em class="placeholder">9</em>.',
+      ],
+    ];
+
+    yield 'INVALID: depth too high' => [
+      0,
+      12,
+      [
+        'settings.depth' => 'This value should be between <em class="placeholder">1</em> and <em class="placeholder">9</em>.',
+      ],
+    ];
+
+    yield 'INVALID: depth too low' => [
+      0,
+      0,
+      [
+        'settings.depth' => 'This value should be between <em class="placeholder">1</em> and <em class="placeholder">9</em>.',
+      ],
+    ];
+
+    yield 'INVALID: start at third level, depth too high' => [
+      2,
+      9,
+      [
+        'settings.depth' => 'This value should be between <em class="placeholder">1</em> and <em class="placeholder">7</em>.',
+      ],
+    ];
+
+    yield 'OK: deepest level only' => [9, 1, []];
+
+    yield 'INVALID: start at deepest level, depth too high' => [
+      9,
+      2,
+      [
+        'settings.depth' => 'This value should be between <em class="placeholder">1</em> and <em class="placeholder">1</em>.',
+      ],
+    ];
+  }
+
+  /**
+   * Tests validating menu block `level` and `depth` settings.
+   *
+   * @dataProvider providerMenuBlockLevelAndDepth
+   */
+  public function testMenuBlockLevelAndDepth(int $level, ?int $depth, array $expected_errors): void {
+    $this->installConfig('system');
+
+    $this->entity = Block::create([
+      'id' => 'account_menu',
+      'theme' => 'stark',
+      'plugin' => 'system_menu_block:account',
+      'settings' => [
+        'id' => 'system_menu_block:account',
+        'label' => 'Account Menu',
+        'label_display' => FALSE,
+        'provider' => 'system',
+        'level' => $level,
+        'depth' => $depth,
+        'expand_all_items' => FALSE,
+      ],
+      'region' => 'content',
+    ]);
+
+    $this->assertValidationErrors($expected_errors);
+  }
+
+}

web/core/modules/block/tests/src/Kernel/BlockViewBuilderTest.php

@@ -0,0 +1,383 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\Component\Utility\Html;
+use Drupal\Core\Cache\Cache;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\Language\LanguageInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\block\Entity\Block;
+
+/**
+ * Tests the block view builder.
+ *
+ * @group block
+ */
+class BlockViewBuilderTest extends KernelTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'block_test', 'system', 'user'];
+
+  /**
+   * The block being tested.
+   *
+   * @var \Drupal\block\BlockInterface
+   */
+  protected $block;
+
+  /**
+   * The block storage.
+   *
+   * @var \Drupal\Core\Config\Entity\ConfigEntityStorageInterface
+   */
+  protected $controller;
+
+  /**
+   * The renderer.
+   *
+   * @var \Drupal\Core\Render\RendererInterface
+   */
+  protected $renderer;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->container->get('theme_installer')->install(['stark']);
+    $this->controller = $this->container
+      ->get('entity_type.manager')
+      ->getStorage('block');
+
+    \Drupal::keyValue('block_test')->set('content', 'Llamas &gt; unicorns!');
+
+    // Create a block with only required values.
+    $this->block = $this->controller->create([
+      'id' => 'test_block',
+      'theme' => 'stark',
+      'plugin' => 'test_cache',
+    ]);
+    $this->block->save();
+
+    $this->container->get('cache.render')->deleteAll();
+
+    $this->renderer = $this->container->get('renderer');
+  }
+
+  /**
+   * Tests rendering a block plugin that returns an empty array.
+   */
+  public function testEmptyRender(): void {
+    \Drupal::keyValue('block_test')->set('content', '');
+
+    $entity = $this->controller->create([
+      'id' => 'test_block1',
+      'theme' => 'stark',
+      'plugin' => 'test_empty',
+    ]);
+    $entity->save();
+
+    // Test the rendering of a block.
+    $entity = Block::load('test_block1');
+    $builder = \Drupal::entityTypeManager()->getViewBuilder('block');
+    $output = $builder->view($entity, 'block');
+    $expected_output = '';
+    $this->assertSame($expected_output, (string) $this->renderer->renderRoot($output));
+  }
+
+  /**
+   * Tests the rendering of blocks.
+   */
+  public function testBasicRendering(): void {
+    \Drupal::keyValue('block_test')->set('content', '');
+
+    $entity = $this->controller->create([
+      'id' => 'test_block1',
+      'theme' => 'stark',
+      'plugin' => 'test_html',
+    ]);
+    $entity->save();
+
+    // Test the rendering of a block.
+    $entity = Block::load('test_block1');
+    $builder = \Drupal::entityTypeManager()->getViewBuilder('block');
+    $output = $builder->view($entity, 'block');
+    $expected = [];
+    $expected[] = '<div id="block-test-block1">';
+    $expected[] = '  ';
+    $expected[] = '    ';
+    $expected[] = '      ';
+    $expected[] = '  </div>';
+    $expected[] = '';
+    $expected_output = implode("\n", $expected);
+    $this->assertSame($expected_output, (string) $this->renderer->renderRoot($output));
+
+    // Reset the HTML IDs so that the next render is not affected.
+    Html::resetSeenIds();
+
+    // Test the rendering of a block with a given title.
+    $entity = $this->controller->create([
+      'id' => 'test_block2',
+      'theme' => 'stark',
+      'plugin' => 'test_html',
+      'settings' => [
+        'label' => 'Powered by Bananas',
+      ],
+    ]);
+    $entity->save();
+    $output = $builder->view($entity, 'block');
+    $expected = [];
+    $expected[] = '<div id="block-test-block2">';
+    $expected[] = '  ';
+    $expected[] = '      <h2>Powered by Bananas</h2>';
+    $expected[] = '    ';
+    $expected[] = '      ';
+    $expected[] = '  </div>';
+    $expected[] = '';
+    $expected_output = implode("\n", $expected);
+    $this->assertSame($expected_output, (string) $this->renderer->renderRoot($output));
+  }
+
+  /**
+   * Tests block render cache handling.
+   */
+  public function testBlockViewBuilderCache(): void {
+    // Verify cache handling for a non-empty block.
+    $this->verifyRenderCacheHandling();
+
+    // Create an empty block.
+    $this->block = $this->controller->create([
+      'id' => 'test_block',
+      'theme' => 'stark',
+      'plugin' => 'test_cache',
+    ]);
+    $this->block->save();
+    \Drupal::keyValue('block_test')->set('content', NULL);
+
+    // Verify cache handling for an empty block.
+    $this->verifyRenderCacheHandling();
+  }
+
+  /**
+   * Tests title block render cache handling.
+   *
+   * @see \Drupal\block_test\Hook\BlockTestHooks::blockViewPageTitleBlockAlter()
+   */
+  public function testBlockViewBuilderCacheTitleBlock(): void {
+    // Create title block.
+    $this->block = $this->controller->create([
+      'id' => 'test_block_title',
+      'theme' => 'stark',
+      'plugin' => 'page_title_block',
+    ]);
+    $this->block->save();
+
+    $entity = Block::load('test_block_title');
+    $builder = \Drupal::entityTypeManager()->getViewBuilder('block');
+    $output = $builder->view($entity, 'block');
+
+    $this->assertSame(
+      ['block_view', 'config:block.block.test_block_title', 'custom_cache_tag'],
+      $output['#cache']['tags']
+    );
+  }
+
+  /**
+   * Verifies render cache handling of the block being tested.
+   *
+   * @see ::testBlockViewBuilderCache()
+   */
+  protected function verifyRenderCacheHandling(): void {
+    /** @var \Drupal\Core\Cache\VariationCacheFactoryInterface $variation_cache_factory */
+    $variation_cache_factory = $this->container->get('variation_cache_factory');
+    $cache_bin = $variation_cache_factory->get('render');
+
+    // Force a request via GET so we can test the render cache.
+    $request = \Drupal::request();
+    $request_method = $request->server->get('REQUEST_METHOD');
+    $request->setMethod('GET');
+
+    // Test that a cache entry is created.
+    $build = $this->getBlockRenderArray();
+    $cache_keys = ['entity_view', 'block', 'test_block'];
+    $this->renderer->renderRoot($build);
+    $this->assertNotEmpty($cache_bin->get($cache_keys, CacheableMetadata::createFromRenderArray($build)), 'The block render element has been cached.');
+
+    // Re-save the block and check that the cache entry has been deleted.
+    $this->block->save();
+    $this->assertFalse($cache_bin->get($cache_keys, CacheableMetadata::createFromRenderArray($build)), 'The block render cache entry has been cleared when the block was saved.');
+
+    // Rebuild the render array (creating a new cache entry in the process) and
+    // delete the block to check the cache entry is deleted.
+    unset($build['#printed']);
+    // Re-add the block because \Drupal\block\BlockViewBuilder::buildBlock()
+    // removes it.
+    $build['#block'] = $this->block;
+
+    $this->renderer->renderRoot($build);
+    $this->assertNotEmpty($cache_bin->get($cache_keys, CacheableMetadata::createFromRenderArray($build)), 'The block render element has been cached.');
+    $this->block->delete();
+    $this->assertFalse($cache_bin->get($cache_keys, CacheableMetadata::createFromRenderArray($build)), 'The block render cache entry has been cleared when the block was deleted.');
+
+    // Restore the previous request method.
+    $request->setMethod($request_method);
+  }
+
+  /**
+   * Tests block view altering.
+   *
+   * @see hook_block_view_alter()
+   * @see hook_block_view_BASE_BLOCK_ID_alter()
+   */
+  public function testBlockViewBuilderViewAlter(): void {
+    // Establish baseline.
+    $build = $this->getBlockRenderArray();
+    $this->setRawContent((string) $this->renderer->renderRoot($build));
+    $this->assertSame('Llamas > unicorns!', trim((string) $this->cssSelect('div')[0]));
+
+    // Enable the block view alter hook that adds a foo=bar attribute.
+    \Drupal::state()->set('block_test_view_alter_suffix', TRUE);
+    Cache::invalidateTags($this->block->getCacheTagsToInvalidate());
+    $build = $this->getBlockRenderArray();
+    $this->setRawContent((string) $this->renderer->renderRoot($build));
+    $this->assertSame('Llamas > unicorns!', trim((string) $this->cssSelect('[foo=bar]')[0]));
+    \Drupal::state()->set('block_test_view_alter_suffix', FALSE);
+
+    \Drupal::keyValue('block_test')->set('content', NULL);
+    Cache::invalidateTags($this->block->getCacheTagsToInvalidate());
+
+    // Advanced: cached block, but an alter hook adds a #pre_render callback to
+    // alter the eventual content.
+    \Drupal::state()->set('block_test_view_alter_append_pre_render_prefix', TRUE);
+    $build = $this->getBlockRenderArray();
+    $this->assertFalse(isset($build['#prefix']), 'The appended #pre_render callback has not yet run before rendering.');
+    $this->assertSame('Hiya!<br>', (string) $this->renderer->renderRoot($build));
+    // Check that a cached block without content is altered.
+    $this->assertArrayHasKey('#prefix', $build);
+    $this->assertSame('Hiya!<br>', $build['#prefix']);
+  }
+
+  /**
+   * Tests block build altering.
+   *
+   * @see hook_block_build_alter()
+   * @see hook_block_build_BASE_BLOCK_ID_alter()
+   */
+  public function testBlockViewBuilderBuildAlter(): void {
+    // Force a request via GET so we can test the render cache.
+    $request = \Drupal::request();
+    $request_method = $request->server->get('REQUEST_METHOD');
+    $request->setMethod('GET');
+
+    $default_keys = ['entity_view', 'block', 'test_block'];
+    $default_contexts = [];
+    $default_tags = ['block_view', 'config:block.block.test_block'];
+    $default_max_age = Cache::PERMANENT;
+
+    // hook_block_build_alter() adds an additional cache key.
+    $alter_add_key = $this->randomMachineName();
+    \Drupal::state()->set('block_test_block_alter_cache_key', $alter_add_key);
+    $this->assertBlockRenderedWithExpectedCacheability(array_merge($default_keys, [$alter_add_key]), $default_contexts, $default_tags, $default_max_age);
+    \Drupal::state()->set('block_test_block_alter_cache_key', NULL);
+
+    // hook_block_build_alter() adds an additional cache context.
+    $alter_add_context = 'url.query_args:' . $this->randomMachineName();
+    \Drupal::state()->set('block_test_block_alter_cache_context', $alter_add_context);
+    $this->assertBlockRenderedWithExpectedCacheability($default_keys, Cache::mergeContexts($default_contexts, [$alter_add_context]), $default_tags, $default_max_age);
+    \Drupal::state()->set('block_test_block_alter_cache_context', NULL);
+
+    // hook_block_build_alter() adds an additional cache tag.
+    $alter_add_tag = $this->randomMachineName();
+    \Drupal::state()->set('block_test_block_alter_cache_tag', $alter_add_tag);
+    $this->assertBlockRenderedWithExpectedCacheability($default_keys, $default_contexts, Cache::mergeTags($default_tags, [$alter_add_tag]), $default_max_age);
+    \Drupal::state()->set('block_test_block_alter_cache_tag', NULL);
+
+    // hook_block_build_alter() alters the max-age.
+    $alter_max_age = 300;
+    \Drupal::state()->set('block_test_block_alter_cache_max_age', $alter_max_age);
+    $this->assertBlockRenderedWithExpectedCacheability($default_keys, $default_contexts, $default_tags, $alter_max_age);
+    \Drupal::state()->set('block_test_block_alter_cache_max_age', NULL);
+
+    // hook_block_build_alter() alters cache keys, contexts, tags and max-age.
+    \Drupal::state()->set('block_test_block_alter_cache_key', $alter_add_key);
+    \Drupal::state()->set('block_test_block_alter_cache_context', $alter_add_context);
+    \Drupal::state()->set('block_test_block_alter_cache_tag', $alter_add_tag);
+    \Drupal::state()->set('block_test_block_alter_cache_max_age', $alter_max_age);
+    $this->assertBlockRenderedWithExpectedCacheability(array_merge($default_keys, [$alter_add_key]), Cache::mergeContexts($default_contexts, [$alter_add_context]), Cache::mergeTags($default_tags, [$alter_add_tag]), $alter_max_age);
+    \Drupal::state()->set('block_test_block_alter_cache_key', NULL);
+    \Drupal::state()->set('block_test_block_alter_cache_context', NULL);
+    \Drupal::state()->set('block_test_block_alter_cache_tag', NULL);
+    \Drupal::state()->set('block_test_block_alter_cache_max_age', NULL);
+
+    // hook_block_build_alter() sets #create_placeholder.
+    foreach ([TRUE, FALSE] as $value) {
+      \Drupal::state()->set('block_test_block_alter_create_placeholder', $value);
+      $build = $this->getBlockRenderArray();
+      $this->assertTrue(isset($build['#create_placeholder']));
+      $this->assertSame($value, $build['#create_placeholder']);
+    }
+    \Drupal::state()->set('block_test_block_alter_create_placeholder', NULL);
+
+    // Restore the previous request method.
+    $request->setMethod($request_method);
+  }
+
+  /**
+   * Asserts that a block is built/rendered/cached with expected cacheability.
+   *
+   * @param string[] $expected_keys
+   *   The expected cache keys.
+   * @param string[] $expected_contexts
+   *   The expected cache contexts.
+   * @param string[] $expected_tags
+   *   The expected cache tags.
+   * @param int $expected_max_age
+   *   The expected max-age.
+   *
+   * @internal
+   */
+  protected function assertBlockRenderedWithExpectedCacheability(array $expected_keys, array $expected_contexts, array $expected_tags, int $expected_max_age): void {
+    /** @var \Drupal\Core\Cache\VariationCacheFactoryInterface $variation_cache_factory */
+    $variation_cache_factory = $this->container->get('variation_cache_factory');
+    $cache_bin = $variation_cache_factory->get('render');
+
+    $required_cache_contexts = ['languages:' . LanguageInterface::TYPE_INTERFACE, 'theme', 'user.permissions'];
+
+    // Check that the expected cacheability metadata is present in:
+    // - the built render array;
+    $build = $this->getBlockRenderArray();
+    $this->assertSame($expected_keys, $build['#cache']['keys']);
+    $this->assertEqualsCanonicalizing($expected_contexts, $build['#cache']['contexts']);
+    $this->assertEqualsCanonicalizing($expected_tags, $build['#cache']['tags']);
+    $this->assertSame($expected_max_age, $build['#cache']['max-age']);
+    $this->assertFalse(isset($build['#create_placeholder']));
+    // - the rendered render array;
+    $this->renderer->renderRoot($build);
+    // - the render cache item.
+    $final_cache_contexts = Cache::mergeContexts($expected_contexts, $required_cache_contexts);
+    $cache_item = $cache_bin->get($expected_keys, CacheableMetadata::createFromRenderArray($build));
+    $this->assertNotEmpty($cache_item, 'The block render element has been cached with the expected cache keys.');
+    $this->assertEqualsCanonicalizing(Cache::mergeTags($expected_tags, ['rendered']), $cache_item->tags);
+    $this->assertEqualsCanonicalizing($final_cache_contexts, $cache_item->data['#cache']['contexts']);
+    $this->assertEqualsCanonicalizing($expected_tags, $cache_item->data['#cache']['tags']);
+    $this->assertSame($expected_max_age, $cache_item->data['#cache']['max-age']);
+
+    $cache_bin->delete($expected_keys, CacheableMetadata::createFromRenderArray($build));
+  }
+
+  /**
+   * Get a fully built render array for a block.
+   *
+   * @return array
+   *   The render array.
+   */
+  protected function getBlockRenderArray() {
+    return $this->container->get('entity_type.manager')->getViewBuilder('block')->view($this->block, 'block');
+  }
+
+}

web/core/modules/block/tests/src/Kernel/ConfigActionsTest.php

@@ -0,0 +1,222 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\block\Entity\Block;
+use Drupal\Component\Plugin\Exception\PluginNotFoundException;
+use Drupal\Core\Config\Action\ConfigActionException;
+use Drupal\Core\Config\Action\ConfigActionManager;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Extension\ThemeInstallerInterface;
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\Tests\block\Traits\BlockCreationTrait;
+
+/**
+ * @covers \Drupal\block\Plugin\ConfigAction\PlaceBlock
+ * @covers \Drupal\block\Plugin\ConfigAction\PlaceBlockDeriver
+ * @group block
+ */
+class ConfigActionsTest extends KernelTestBase {
+
+  use BlockCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'system', 'user'];
+
+  /**
+   * The configuration action manager.
+   */
+  private readonly ConfigActionManager $configActionManager;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->container->get(ThemeInstallerInterface::class)->install([
+      'olivero',
+      'claro',
+      'umami',
+    ]);
+    $this->config('system.theme')
+      ->set('default', 'olivero')
+      ->set('admin', 'claro')
+      ->save();
+    $this->configActionManager = $this->container->get('plugin.manager.config_action');
+  }
+
+  /**
+   * Tests the application of entity method actions on a block.
+   */
+  public function testEntityMethodActions(): void {
+    $block = $this->placeBlock('system_messages_block', ['theme' => 'olivero']);
+    $this->assertSame('content', $block->getRegion());
+    $this->assertSame(0, $block->getWeight());
+
+    $this->configActionManager->applyAction(
+      'entity_method:block.block:setRegion',
+      $block->getConfigDependencyName(),
+      'highlighted',
+    );
+    $this->configActionManager->applyAction(
+      'entity_method:block.block:setWeight',
+      $block->getConfigDependencyName(),
+      -10,
+    );
+
+    $block = Block::load($block->id());
+    $this->assertSame('highlighted', $block->getRegion());
+    $this->assertSame(-10, $block->getWeight());
+  }
+
+  /**
+   * @testWith ["placeBlockInDefaultTheme"]
+   *           ["placeBlockInAdminTheme"]
+   */
+  public function testPlaceBlockActionOnlyWorksOnBlocks(string $action): void {
+    $this->expectException(PluginNotFoundException::class);
+    $this->expectExceptionMessage("The \"user_role\" entity does not support the \"$action\" config action.");
+    $this->configActionManager->applyAction($action, 'user.role.anonymous', []);
+  }
+
+  /**
+   * Verifies placeBlockInDefaultTheme action doesn't alter an existing block.
+   */
+  public function testPlaceBlockActionDoesNotChangeExistingBlock(): void {
+    $extant_region = Block::load('olivero_powered')->getRegion();
+    $this->assertNotSame('content', $extant_region);
+
+    $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.olivero_powered', [
+      'plugin' => 'system_powered_by_block',
+      'region' => [
+        'olivero' => 'content',
+      ],
+    ]);
+    // The extant block should be unchanged.
+    $this->assertSame($extant_region, Block::load('olivero_powered')->getRegion());
+  }
+
+  /**
+   * @testWith ["placeBlockInDefaultTheme", "olivero", "header"]
+   *           ["placeBlockInAdminTheme", "claro", "page_bottom"]
+   */
+  public function testPlaceBlockInDynamicRegion(string $action, string $expected_theme, string $expected_region): void {
+    $this->configActionManager->applyAction($action, 'block.block.test_block', [
+      'plugin' => 'system_powered_by_block',
+      'region' => [
+        'olivero' => 'header',
+        'claro' => 'page_bottom',
+      ],
+      'default_region' => 'content',
+    ]);
+
+    $block = Block::load('test_block');
+    $this->assertInstanceOf(Block::class, $block);
+    $this->assertSame('system_powered_by_block', $block->getPluginId());
+    $this->assertSame($expected_theme, $block->getTheme());
+    $this->assertSame($expected_region, $block->getRegion());
+
+    $this->expectException(ConfigActionException::class);
+    $this->expectExceptionMessage('Cannot determine which region to place this block into, because no default region was provided.');
+    $this->configActionManager->applyAction($action, 'block.block.no_region', [
+      'plugin' => 'system_powered_by_block',
+      'region' => [],
+    ]);
+  }
+
+  /**
+   * @testWith ["placeBlockInDefaultTheme", "olivero"]
+   *           ["placeBlockInAdminTheme", "claro"]
+   */
+  public function testPlaceBlockInStaticRegion(string $action, string $expected_theme): void {
+    $this->configActionManager->applyAction($action, 'block.block.test_block', [
+      'plugin' => 'system_powered_by_block',
+      'region' => 'content',
+    ]);
+
+    $block = Block::load('test_block');
+    $this->assertInstanceOf(Block::class, $block);
+    $this->assertSame('system_powered_by_block', $block->getPluginId());
+    $this->assertSame($expected_theme, $block->getTheme());
+    $this->assertSame('content', $block->getRegion());
+  }
+
+  /**
+   * Tests placing a block in the default theme's region.
+   */
+  public function testPlaceBlockInDefaultRegion(): void {
+    $this->config('system.theme')->set('default', 'umami')->save();
+    $this->testPlaceBlockInDynamicRegion('placeBlockInDefaultTheme', 'umami', 'content');
+  }
+
+  /**
+   * Tests placing a block at the first and last position in a region.
+   */
+  public function testPlaceBlockAtPosition(): void {
+    // Ensure there's at least one block already in the region.
+    $block = Block::create([
+      'id' => 'block_1',
+      'theme' => 'olivero',
+      'region' => 'content_above',
+      'weight' => 0,
+      'plugin' => 'system_powered_by_block',
+    ]);
+    $block->save();
+
+    $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.first', [
+      'plugin' => $block->getPluginId(),
+      'region' => [
+        $block->getTheme() => $block->getRegion(),
+      ],
+      'position' => 'first',
+    ]);
+    $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.last', [
+      'plugin' => $block->getPluginId(),
+      'region' => [
+        $block->getTheme() => $block->getRegion(),
+      ],
+      'position' => 'last',
+    ]);
+
+    // Query for blocks in the region, ordered by weight.
+    $blocks = $this->container->get(EntityTypeManagerInterface::class)
+      ->getStorage('block')
+      ->getQuery()
+      ->condition('theme', $block->getTheme())
+      ->condition('region', $block->getRegion())
+      ->sort('weight', 'ASC')
+      ->execute();
+    $this->assertGreaterThanOrEqual(3, $blocks);
+    $this->assertSame('first', key($blocks));
+    $this->assertSame('last', end($blocks));
+  }
+
+  /**
+   * Tests using the PlaceBlock action in an empty region.
+   */
+  public function testPlaceBlockInEmptyRegion(): void {
+    /** @var \Drupal\Core\Entity\Query\QueryInterface $query */
+    $query = $this->container->get(EntityTypeManagerInterface::class)
+      ->getStorage('block')
+      ->getQuery()
+      ->count()
+      ->condition('theme', 'olivero')
+      ->condition('region', 'footer_top');
+    $this->assertSame(0, $query->execute());
+
+    // Place a block in that region.
+    $this->configActionManager->applyAction('placeBlockInDefaultTheme', 'block.block.test', [
+      'plugin' => 'system_powered_by_block',
+      'region' => [
+        'olivero' => 'footer_top',
+      ],
+      'position' => 'first',
+    ]);
+    $this->assertSame(1, $query->execute());
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Migrate/d6/MigrateBlockContentTranslationTest.php

@@ -0,0 +1,69 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Migrate\d6;
+
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+use Drupal\block\Hook\BlockHooks;
+
+/**
+ * Tests migration of i18n block translations.
+ *
+ * @group migrate_drupal_6
+ */
+class MigrateBlockContentTranslationTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'comment',
+    'views',
+    'block_content',
+    'config_translation',
+    'language',
+    'locale',
+    'path_alias',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('block_content');
+    $this->installEntitySchema('path_alias');
+    $this->installConfig(['block']);
+    $this->installConfig(['block_content']);
+    $this->container->get('theme_installer')->install(['stark']);
+
+    $this->executeMigrations([
+      'language',
+      'd6_filter_format',
+      'block_content_type',
+      'block_content_body_field',
+      'd6_menu',
+      'd6_custom_block',
+      'd6_user_role',
+      'd6_block',
+      'd6_block_translation',
+    ]);
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+  }
+
+  /**
+   * Tests the migration of block title translation.
+   */
+  public function testBlockContentTranslation(): void {
+    /** @var \Drupal\language\ConfigurableLanguageManagerInterface $language_manager */
+    $language_manager = $this->container->get('language_manager');
+
+    $config = $language_manager->getLanguageConfigOverride('zu', 'block.block.user_1');
+    $this->assertSame('zu - Navigation', $config->get('settings.label'));
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Migrate/d6/MigrateBlockTest.php

@@ -0,0 +1,321 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Migrate\d6;
+
+use Drupal\block\Entity\Block;
+use Drupal\Tests\migrate_drupal\Kernel\d6\MigrateDrupal6TestBase;
+use Drupal\block\Hook\BlockHooks;
+
+/**
+ * Tests migration of blocks to configuration entities.
+ *
+ * @group migrate_drupal_6
+ */
+class MigrateBlockTest extends MigrateDrupal6TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'views',
+    'comment',
+    'menu_ui',
+    'block_content',
+    'taxonomy',
+    'node',
+    'path_alias',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('path_alias');
+
+    // Install the themes used for this test.
+    $this->installEntitySchema('block_content');
+    $this->container->get('theme_installer')->install(['olivero', 'test_theme']);
+
+    $this->installConfig(['block_content']);
+
+    // Set Olivero as the default public theme.
+    $config = $this->config('system.theme');
+    $config->set('default', 'olivero');
+    $config->save();
+
+    $this->executeMigrations([
+      'd6_filter_format',
+      'block_content_type',
+      'block_content_body_field',
+      'd6_menu',
+      'd6_custom_block',
+      'd6_user_role',
+      'd6_block',
+    ]);
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+  }
+
+  /**
+   * Asserts various aspects of a block.
+   *
+   * @param string $id
+   *   The block ID.
+   * @param array $visibility
+   *   The block visibility settings.
+   * @param string $region
+   *   The display region.
+   * @param string $theme
+   *   The theme.
+   * @param int $weight
+   *   The block weight.
+   * @param array $settings
+   *   (optional) The block settings.
+   * @param bool $status
+   *   Whether the block is expected to be enabled or disabled.
+   *
+   * @internal
+   */
+  public function assertEntity(string $id, array $visibility, string $region, string $theme, int $weight, ?array $settings = NULL, bool $status = TRUE): void {
+    $block = Block::load($id);
+    $this->assertInstanceOf(Block::class, $block);
+    $this->assertSame($visibility, $block->getVisibility());
+    $this->assertSame($region, $block->getRegion());
+    $this->assertSame($theme, $block->getTheme());
+    $this->assertSame($weight, $block->getWeight());
+    $this->assertSame($status, $block->status());
+    if ($settings) {
+      $block_settings = $block->get('settings');
+      $block_settings['id'] = current(explode(':', $block_settings['id']));
+      $this->assertEquals($settings, $block_settings);
+    }
+  }
+
+  /**
+   * Tests the block migration.
+   */
+  public function testBlockMigration(): void {
+    $blocks = Block::loadMultiple();
+    $this->assertCount(24, $blocks);
+
+    // Check user blocks.
+    $visibility = [
+      'request_path' => [
+        'id' => 'request_path',
+        'negate' => TRUE,
+        'pages' => "<front>\n/node/1\n/blog/*",
+      ],
+    ];
+    $settings = [
+      'id' => 'user_login_block',
+      'label' => '',
+      'provider' => 'user',
+      'label_display' => '0',
+    ];
+    $this->assertEntity('user', $visibility, 'sidebar', 'olivero', -10, $settings);
+
+    $visibility = [];
+    $settings = [
+      'id' => 'system_menu_block',
+      'label' => 'zu - Navigation',
+      'provider' => 'system',
+      'label_display' => 'visible',
+      'level' => 1,
+      'expand_all_items' => FALSE,
+      'depth' => 0,
+    ];
+    $this->assertEntity('user_1', $visibility, 'sidebar', 'olivero', -11, $settings);
+
+    $visibility = [
+      'user_role' => [
+        'id' => 'user_role',
+        'negate' => FALSE,
+        'context_mapping' => [
+          'user' => '@user.current_user_context:current_user',
+        ],
+        'roles' => [
+          'authenticated' => 'authenticated',
+        ],
+      ],
+    ];
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'items_per_page' => '5',
+    ];
+    $this->assertEntity('user_2', $visibility, 'sidebar', 'olivero', -11, $settings);
+
+    $visibility = [
+      'user_role' => [
+        'id' => 'user_role',
+        'negate' => FALSE,
+        'context_mapping' => [
+          'user' => '@user.current_user_context:current_user',
+        ],
+        'roles' => [
+          'migrate_test_role_1' => 'migrate_test_role_1',
+        ],
+      ],
+    ];
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'items_per_page' => '10',
+    ];
+    $this->assertEntity('user_3', $visibility, 'sidebar', 'olivero', -10, $settings);
+
+    // Check system block.
+    $visibility = [
+      'request_path' => [
+        'id' => 'request_path',
+        'negate' => TRUE,
+        'pages' => '/node/1',
+      ],
+    ];
+    $settings = [
+      'id' => 'system_powered_by_block',
+      'label' => '',
+      'provider' => 'system',
+      'label_display' => '0',
+    ];
+    $this->assertEntity('system', $visibility, 'footer_top', 'olivero', -5, $settings);
+
+    // Check menu blocks.
+    $settings = [
+      'id' => 'system_menu_block',
+      'label' => '',
+      'provider' => 'system',
+      'label_display' => '0',
+      'level' => 1,
+      'depth' => NULL,
+      'expand_all_items' => FALSE,
+    ];
+    $this->assertEntity('menu', [], 'header', 'olivero', -5, $settings);
+
+    // Check aggregator block.
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'block_count' => 7,
+      'feed' => '5',
+    ];
+    $this->assertEntity('aggregator', [], 'sidebar', 'olivero', -2, $settings);
+
+    // Check book block.
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'block_mode' => 'book pages',
+    ];
+    $this->assertEntity('book', [], 'sidebar', 'olivero', -4, $settings);
+
+    // Check forum block settings.
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'block_count' => 3,
+    ];
+    $this->assertEntity('forum', [], 'sidebar', 'olivero', -8, $settings);
+
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'block_count' => 4,
+    ];
+    $this->assertEntity('forum_1', [], 'sidebar', 'olivero', -9, $settings);
+
+    // Check statistic block settings.
+    $settings = [
+      'id' => 'broken',
+      'label' => '',
+      'provider' => 'core',
+      'label_display' => '0',
+      'top_day_num' => 7,
+      'top_all_num' => 8,
+      'top_last_num' => 9,
+    ];
+    $this->assertEntity('statistics', [], 'sidebar', 'olivero', 0, $settings);
+
+    // Check content blocks.
+    $visibility = [
+      'request_path' => [
+        'id' => 'request_path',
+        'negate' => FALSE,
+        'pages' => '<front>',
+      ],
+    ];
+    $settings = [
+      'id' => 'block_content',
+      'label' => 'Static Block',
+      'provider' => 'block_content',
+      'label_display' => 'visible',
+      'status' => TRUE,
+      'info' => '',
+      'view_mode' => 'full',
+    ];
+    $this->assertEntity('block', $visibility, 'content', 'olivero', 0, $settings);
+
+    $visibility = [
+      'request_path' => [
+        'id' => 'request_path',
+        'negate' => FALSE,
+        'pages' => '/node',
+      ],
+    ];
+    $settings = [
+      'id' => 'block_content',
+      'label' => 'Another Static Block',
+      'provider' => 'block_content',
+      'label_display' => 'visible',
+      'status' => TRUE,
+      'info' => '',
+      'view_mode' => 'full',
+    ];
+    // We expect this block to be disabled because '' is not a valid region,
+    // and block_rebuild() will disable any block in an invalid region.
+    $this->assertEntity('block_1', $visibility, '', 'bluemarine', -4, $settings, FALSE);
+
+    $settings = [
+      'id' => 'block_content',
+      'label' => '',
+      'provider' => 'block_content',
+      'label_display' => '0',
+      'status' => TRUE,
+      'info' => '',
+      'view_mode' => 'full',
+    ];
+    $this->assertEntity('block_2', [], 'right', 'test_theme', -7, $settings);
+
+    // Content block with php code is not migrated.
+    $block = Block::load('block_3');
+    $this->assertNotInstanceOf(Block::class, $block);
+
+    // Check migrate messages.
+    $messages = iterator_to_array($this->getMigration('d6_block')->getIdMap()->getMessages());
+    $this->assertCount(7, $messages);
+    $this->assertSame($messages[0]->message, 'Schema errors for block.block.block_1 with the following errors: 0 [dependencies.theme.0] Theme &#039;bluemarine&#039; is not installed., 1 [theme] Theme &#039;bluemarine&#039; is not installed., 2 [region] This value should not be blank., 3 [region] This is not a valid region of the &lt;em class=&quot;placeholder&quot;&gt;bluemarine&lt;/em&gt; theme.');
+    $this->assertSame($messages[1]->message, "d6_block:visibility: The block with bid '13' from module 'block' will have no PHP or request_path visibility configuration.");
+    $this->assertSame($messages[2]->message, 'Schema errors for block.block.aggregator with the following errors: block.block.aggregator:settings.block_count missing schema, block.block.aggregator:settings.feed missing schema, 0 [settings.feed] &#039;feed&#039; is not a supported key., 1 [settings] &#039;block_count&#039; is an unknown key because plugin is aggregator_feed_block (see config schema type block.settings.*).');
+    $this->assertSame($messages[3]->message, 'Schema errors for block.block.book with the following errors: block.block.book:settings.block_mode missing schema, 0 [settings.block_mode] &#039;block_mode&#039; is not a supported key.');
+    $this->assertSame('Schema errors for block.block.forum with the following errors: block.block.forum:settings.block_count missing schema, 0 [settings] &#039;block_count&#039; is an unknown key because plugin is forum_active_block (see config schema type block.settings.*).', $messages[4]->message);
+    $this->assertSame('Schema errors for block.block.forum_1 with the following errors: block.block.forum_1:settings.block_count missing schema, 0 [settings] &#039;block_count&#039; is an unknown key because plugin is forum_new_block (see config schema type block.settings.*).', $messages[5]->message);
+    $this->assertSame('Schema errors for block.block.statistics with the following errors: block.block.statistics:settings.top_day_num missing schema, block.block.statistics:settings.top_all_num missing schema, block.block.statistics:settings.top_last_num missing schema, 0 [settings.top_day_num] &#039;top_day_num&#039; is not a supported key., 1 [settings.top_all_num] &#039;top_all_num&#039; is not a supported key., 2 [settings.top_last_num] &#039;top_last_num&#039; is not a supported key.', $messages[6]->message);
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Migrate/d7/MigrateBlockContentTranslationTest.php

@@ -0,0 +1,74 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Migrate\d7;
+
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+use Drupal\block\Hook\BlockHooks;
+
+/**
+ * Tests migration of i18n block translations.
+ *
+ * @group migrate_drupal_7
+ */
+class MigrateBlockContentTranslationTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'node',
+    'text',
+    'block',
+    'comment',
+    'filter',
+    'views',
+    'block_content',
+    'config_translation',
+    'language',
+    'locale',
+    'path_alias',
+    'taxonomy',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('block_content');
+    $this->installEntitySchema('path_alias');
+    $this->installConfig(['block']);
+    $this->installConfig(['block_content']);
+    $this->container->get('theme_installer')->install(['stark']);
+
+    $this->executeMigrations([
+      'language',
+      'd7_filter_format',
+      'block_content_type',
+      'block_content_body_field',
+      'd7_custom_block',
+      'd7_user_role',
+      'd7_block',
+      'd7_block_translation',
+    ]);
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+  }
+
+  /**
+   * Tests the migration of block title translation.
+   */
+  public function testBlockContentTranslation(): void {
+    // @todo Skipped due to frequent random test failures.
+    // See https://www.drupal.org/project/drupal/issues/3389365
+    $this->markTestSkipped();
+    /** @var \Drupal\language\ConfigurableLanguageManagerInterface $language_manager */
+    $language_manager = $this->container->get('language_manager');
+
+    $config = $language_manager->getLanguageConfigOverride('fr', 'block.block.bartik_user_login');
+    $this->assertSame('fr - User login title', $config->get('settings.label'));
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Migrate/d7/MigrateBlockNoBlockContentTest.php

@@ -0,0 +1,166 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Migrate\d7;
+
+use Drupal\block\Entity\Block;
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+use Drupal\block\Hook\BlockHooks;
+
+/**
+ * Tests the migration of blocks without Block Content installed.
+ *
+ * @group block
+ */
+class MigrateBlockNoBlockContentTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'views',
+    'comment',
+    'menu_ui',
+    'node',
+    'text',
+    'filter',
+    'path_alias',
+    'user',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    // Install the themes used for this test.
+    $this->container->get('theme_installer')->install(['olivero', 'claro']);
+
+    $this->installConfig(static::$modules);
+    $this->installEntitySchema('path_alias');
+
+    // Set Olivero and Claro as the default public and admin theme.
+    $config = $this->config('system.theme');
+    $config->set('default', 'olivero');
+    $config->set('admin', 'claro');
+    $config->save();
+
+    $this->executeMigrations([
+      'd7_filter_format',
+      'd7_user_role',
+      'd7_block',
+    ]);
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+  }
+
+  /**
+   * Asserts various aspects of a block.
+   *
+   * @param string $id
+   *   The block ID.
+   * @param string $plugin_id
+   *   The block's plugin ID.
+   * @param array $roles
+   *   Role IDs the block is expected to have.
+   * @param string $pages
+   *   The list of pages on which the block should appear.
+   * @param string $region
+   *   The display region.
+   * @param string $theme
+   *   The theme.
+   * @param int $weight
+   *   The block weight.
+   * @param string $label
+   *   The block label.
+   * @param string $label_display
+   *   The block label display setting.
+   * @param bool $status
+   *   Whether the block is expected to be enabled or disabled.
+   *
+   * @internal
+   */
+  public function assertEntity(string $id, string $plugin_id, array $roles, string $pages, string $region, string $theme, int $weight, string $label, string $label_display, bool $status = TRUE): void {
+    $block = Block::load($id);
+    $this->assertInstanceOf(Block::class, $block);
+    /** @var \Drupal\block\BlockInterface $block */
+    $this->assertSame($plugin_id, $block->getPluginId());
+
+    $visibility = $block->getVisibility();
+    if ($roles) {
+      $this->assertSame($roles, array_values($visibility['user_role']['roles']));
+      $this->assertSame('@user.current_user_context:current_user', $visibility['user_role']['context_mapping']['user']);
+    }
+    if ($pages) {
+      $this->assertSame($pages, $visibility['request_path']['pages']);
+    }
+
+    $this->assertSame($region, $block->getRegion());
+    $this->assertSame($theme, $block->getTheme());
+    $this->assertSame($weight, $block->getWeight());
+    $this->assertSame($status, $block->status());
+
+    $config = $this->config('block.block.' . $id);
+    $this->assertSame($label, $config->get('settings.label'));
+    $this->assertSame($label_display, $config->get('settings.label_display'));
+  }
+
+  /**
+   * Tests the block migration.
+   */
+  public function testBlockMigration(): void {
+    $this->assertEntity('bartik_system_main', 'system_main_block', [], '', 'content', 'olivero', 0, '', '0');
+    $this->assertEntity('bartik_search_form', 'search_form_block', [], '', 'content', 'olivero', -1, '', '0');
+    $this->assertEntity('bartik_user_login', 'user_login_block', [], '', 'content', 'olivero', 0, 'User login title', 'visible');
+    $this->assertEntity('bartik_system_powered_by', 'system_powered_by_block', [], '', 'footer_bottom', 'olivero', 10, '', '0');
+    $this->assertEntity('seven_system_main', 'system_main_block', [], '', 'content', 'claro', 0, '', '0');
+    $this->assertEntity('seven_user_login', 'user_login_block', [], '', 'content', 'claro', 10, 'User login title', 'visible');
+
+    // Assert that disabled blocks (or enabled blocks whose plugin IDs could
+    // be resolved) did not migrate.
+    $non_existent_blocks = [
+      'bartik_system_navigation',
+      'bartik_system_help',
+      'seven_user_new',
+      'seven_search_form',
+      'bartik_comment_recent',
+      'bartik_node_syndicate',
+      'bartik_node_recent',
+      'bartik_shortcut_shortcuts',
+      'bartik_system_management',
+      'bartik_system_user-menu',
+      'bartik_system_main-menu',
+      'bartik_user_new',
+      'bartik_user_online',
+      'seven_comment_recent',
+      'seven_node_syndicate',
+      'seven_shortcut_shortcuts',
+      'seven_system_powered-by',
+      'seven_system_navigation',
+      'seven_system_management',
+      'seven_system_user-menu',
+      'seven_system_main-menu',
+      'seven_user_online',
+      'bartik_blog_recent',
+      'bartik_book_navigation',
+      'bartik_locale_language',
+      'bartik_forum_active',
+      'bartik_forum_new',
+      'seven_blog_recent',
+      'seven_book_navigation',
+      'seven_locale_language',
+      'seven_forum_active',
+      'seven_forum_new',
+      'bartik_menu_menu-test-menu',
+      'bartik_statistics_popular',
+      'seven_menu_menu-test-menu',
+      'seven_statistics_popular',
+      'seven_block_1',
+    ];
+    $this->assertEmpty(Block::loadMultiple($non_existent_blocks));
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Migrate/d7/MigrateBlockTest.php

@@ -0,0 +1,178 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Migrate\d7;
+
+use Drupal\block\Entity\Block;
+use Drupal\block_content\Entity\BlockContent;
+use Drupal\Tests\migrate_drupal\Kernel\d7\MigrateDrupal7TestBase;
+use Drupal\block\Hook\BlockHooks;
+
+/**
+ * Tests migration of blocks to configuration entities.
+ *
+ * @group block
+ */
+class MigrateBlockTest extends MigrateDrupal7TestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'views',
+    'comment',
+    'menu_ui',
+    'block_content',
+    'node',
+    'text',
+    'filter',
+    'path_alias',
+    'user',
+  ];
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->installEntitySchema('path_alias');
+
+    // Install the themes used for this test.
+    $this->installEntitySchema('block_content');
+    $this->container->get('theme_installer')->install(['olivero', 'claro']);
+
+    $this->installConfig(static::$modules);
+
+    // Set Olivero and Claro as the default public and admin theme.
+    $config = $this->config('system.theme');
+    $config->set('default', 'olivero');
+    $config->set('admin', 'claro');
+    $config->save();
+
+    $this->executeMigrations([
+      'd7_filter_format',
+      'd7_user_role',
+      'block_content_type',
+      'block_content_body_field',
+      'd7_custom_block',
+      'd7_block',
+    ]);
+    $blockRebuild = new BlockHooks();
+    $blockRebuild->rebuild();
+  }
+
+  /**
+   * Asserts various aspects of a block.
+   *
+   * @param string $id
+   *   The block ID.
+   * @param string $plugin_id
+   *   The block's plugin ID.
+   * @param array $roles
+   *   Role IDs the block is expected to have.
+   * @param string $pages
+   *   The list of pages on which the block should appear.
+   * @param string $region
+   *   The display region.
+   * @param string $theme
+   *   The theme.
+   * @param int $weight
+   *   The block weight.
+   * @param string $label
+   *   The block label.
+   * @param string $label_display
+   *   The block label display setting.
+   * @param bool $status
+   *   Whether the block is expected to be enabled or disabled.
+   *
+   * @internal
+   */
+  public function assertEntity(string $id, string $plugin_id, array $roles, string $pages, string $region, string $theme, int $weight, string $label, string $label_display, bool $status = TRUE): void {
+    $block = Block::load($id);
+    $this->assertInstanceOf(Block::class, $block);
+    /** @var \Drupal\block\BlockInterface $block */
+    $this->assertSame($plugin_id, $block->getPluginId());
+
+    $visibility = $block->getVisibility();
+    if ($roles) {
+      $this->assertSame($roles, array_values($visibility['user_role']['roles']));
+      $this->assertSame('@user.current_user_context:current_user', $visibility['user_role']['context_mapping']['user']);
+    }
+    if ($pages) {
+      $this->assertSame($pages, $visibility['request_path']['pages']);
+    }
+
+    $this->assertSame($region, $block->getRegion());
+    $this->assertSame($theme, $block->getTheme());
+    $this->assertSame($weight, $block->getWeight());
+    $this->assertSame($status, $block->status());
+
+    $config = $this->config('block.block.' . $id);
+    $this->assertSame($label, $config->get('settings.label'));
+    $this->assertSame($label_display, $config->get('settings.label_display'));
+  }
+
+  /**
+   * Tests the block migration.
+   */
+  public function testBlockMigration(): void {
+    $this->assertEntity('bartik_system_main', 'system_main_block', [], '', 'content', 'olivero', 0, '', '0');
+    $this->assertEntity('bartik_search_form', 'search_form_block', [], '', 'content', 'olivero', -1, '', '0');
+    $this->assertEntity('bartik_user_login', 'user_login_block', [], '', 'content', 'olivero', 0, 'User login title', 'visible');
+    $this->assertEntity('bartik_system_powered_by', 'system_powered_by_block', [], '', 'footer_bottom', 'olivero', 10, '', '0');
+    $this->assertEntity('seven_system_main', 'system_main_block', [], '', 'content', 'claro', 0, '', '0');
+    $this->assertEntity('seven_user_login', 'user_login_block', [], '', 'content', 'claro', 10, 'User login title', 'visible');
+
+    // The d7_custom_block migration should have migrated a block containing a
+    // mildly amusing limerick. We'll need its UUID to determine
+    // bartik_block_1's plugin ID.
+    $uuid = BlockContent::load(1)->uuid();
+    $this->assertEntity('bartik_block_1', 'block_content:' . $uuid, ['authenticated'], '', 'content', 'olivero', 0, 'Mildly amusing limerick of the day', 'visible');
+
+    // Assert that disabled blocks (or enabled blocks whose plugin IDs could
+    // be resolved) did not migrate.
+    $non_existent_blocks = [
+      'bartik_system_navigation',
+      'bartik_system_help',
+      'seven_user_new',
+      'seven_search_form',
+      'bartik_comment_recent',
+      'bartik_node_syndicate',
+      'bartik_node_recent',
+      'bartik_shortcut_shortcuts',
+      'bartik_system_management',
+      'bartik_system_user-menu',
+      'bartik_system_main-menu',
+      'bartik_user_new',
+      'bartik_user_online',
+      'seven_comment_recent',
+      'seven_node_syndicate',
+      'seven_shortcut_shortcuts',
+      'seven_system_powered-by',
+      'seven_system_navigation',
+      'seven_system_management',
+      'seven_system_user-menu',
+      'seven_system_main-menu',
+      'seven_user_online',
+      'bartik_blog_recent',
+      'bartik_book_navigation',
+      'bartik_locale_language',
+      'bartik_forum_active',
+      'bartik_forum_new',
+      'seven_blog_recent',
+      'seven_book_navigation',
+      'seven_locale_language',
+      'seven_forum_active',
+      'seven_forum_new',
+      'bartik_menu_menu-test-menu',
+      'bartik_statistics_popular',
+      'seven_menu_menu-test-menu',
+      'seven_statistics_popular',
+      'seven_block_1',
+    ];
+    $this->assertEmpty(Block::loadMultiple($non_existent_blocks));
+  }
+
+}

web/core/modules/block/tests/src/Kernel/NewDefaultThemeBlocksTest.php

@@ -0,0 +1,189 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel;
+
+use Drupal\KernelTests\KernelTestBase;
+use Drupal\Tests\block\Traits\BlockCreationTrait;
+
+/**
+ * Tests that a new default theme gets blocks.
+ *
+ * @group block
+ */
+class NewDefaultThemeBlocksTest extends KernelTestBase {
+
+  use BlockCreationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = [
+    'block',
+    'system',
+    'user',
+  ];
+
+  /**
+   * The theme installer service.
+   *
+   * @var \Drupal\Core\Extension\ThemeInstallerInterface
+   */
+  protected $themeInstaller;
+
+  /**
+   * The default theme.
+   *
+   * @var string
+   */
+  protected $defaultTheme;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->installConfig(['system']);
+    $this->themeInstaller = $this->container->get('theme_installer');
+    $this->defaultTheme = $this->config('system.theme')->get('default');
+  }
+
+  /**
+   * Check the blocks are correctly copied.
+   *
+   * This tests that blocks are correctly copied by
+   * \Drupal\block\Hook\BlockHooks::themesInstalled().
+   */
+  public function testNewDefaultThemeBlocks(): void {
+    $default_theme = $this->defaultTheme;
+    $theme_installer = $this->themeInstaller;
+    $theme_installer->install([$default_theme]);
+
+    // Add two instances of the user login block.
+    $this->placeBlock('user_login_block', [
+      'id' => $default_theme . '_' . $this->randomMachineName(8),
+    ]);
+    $this->placeBlock('user_login_block', [
+      'id' => $default_theme . '_' . $this->randomMachineName(8),
+    ]);
+
+    // Add an instance of a different block.
+    $this->placeBlock('system_powered_by_block', [
+      'id' => $default_theme . '_' . $this->randomMachineName(8),
+    ]);
+
+    // Install a different theme that does not have blocks.
+    $new_theme = 'test_theme';
+    // The new theme is different from the previous default theme.
+    $this->assertNotEquals($new_theme, $default_theme);
+
+    $theme_installer->install([$new_theme]);
+    $this->config('system.theme')
+      ->set('default', $new_theme)
+      ->save();
+
+    $block_storage = $this->container->get('entity_type.manager')->getStorage('block');
+
+    // Ensure that the new default theme has the same blocks as the previous
+    // default theme.
+    $default_block_names = $block_storage->getQuery()
+      ->accessCheck(FALSE)
+      ->condition('theme', $default_theme)
+      ->execute();
+    $new_blocks = $block_storage->getQuery()
+      ->accessCheck(FALSE)
+      ->condition('theme', $new_theme)
+      ->execute();
+    $this->assertSameSize($default_block_names, $new_blocks);
+
+    foreach ($default_block_names as $default_block_name) {
+      // Remove the matching block from the list of blocks in the new theme.
+      // For example, if the old theme has block.block.stark_admin,
+      // unset block.block.olivero_admin.
+      unset($new_blocks[str_replace($default_theme . '_', $new_theme . '_', $default_block_name)]);
+    }
+    $this->assertEmpty($new_blocks);
+
+    // Install a hidden base theme and ensure blocks are not copied.
+    $base_theme = 'test_base_theme';
+    $theme_installer->install([$base_theme]);
+    $new_blocks = $block_storage->getQuery()
+      ->accessCheck(FALSE)
+      ->condition('theme', $base_theme)
+      ->execute();
+    $this->assertEmpty($new_blocks);
+  }
+
+  /**
+   * Checks that a theme block is still created when same ID exists.
+   */
+  public function testBlockCollision(): void {
+    $default_theme = $this->defaultTheme;
+    $theme_installer = $this->themeInstaller;
+    $theme_installer->install([$default_theme]);
+
+    // Add two instances of the user login block with machine
+    // names that will collide.
+    $this->placeBlock('user_login_block', [
+      'id' => 'user_login_block',
+    ]);
+    $this->placeBlock('user_login_block', [
+      'id' => $default_theme . '_user_login_block',
+    ]);
+
+    // Add an instance of a different block.
+    $this->placeBlock('system_powered_by_block', [
+      'id' => $default_theme . '_' . strtolower($this->randomMachineName(8)),
+    ]);
+
+    // Install a different theme that does not have blocks.
+    $new_theme = 'test_theme';
+    // The new theme is different from the previous default theme.
+    $this->assertNotEquals($new_theme, $default_theme);
+
+    $theme_installer->install([$new_theme]);
+    $this->config('system.theme')
+      ->set('default', $new_theme)
+      ->save();
+
+    $block_storage = $this->container->get('entity_type.manager')->getStorage('block');
+
+    // Ensure that the new default theme has the same blocks as the previous
+    // default theme.
+    $default_block_names = $block_storage->getQuery()
+      ->accessCheck(FALSE)
+      ->condition('theme', $default_theme)
+      ->execute();
+    $new_blocks = $block_storage->getQuery()
+      ->accessCheck(FALSE)
+      ->condition('theme', $new_theme)
+      ->execute();
+    $this->assertSameSize($default_block_names, $new_blocks);
+
+    foreach ($default_block_names as $default_block_name) {
+      // Remove the matching block from the list of blocks in the new theme.
+      // For example, if the old theme has block.block.stark_admin,
+      // unset block.block.olivero_admin.
+      unset($new_blocks[str_replace($default_theme . '_', $new_theme . '_', $default_block_name)]);
+    }
+    // The test_theme_user_login_block machine name is already in use, so
+    // therefore \Drupal\block\BlockRepository::getUniqueMachineName appends a
+    // counter.
+    unset($new_blocks[$new_theme . '_user_login_block_2']);
+    $this->assertEmpty($new_blocks);
+
+    // Install a hidden base theme and ensure blocks are not copied.
+    $base_theme = 'test_base_theme';
+    $theme_installer->install([$base_theme]);
+    $new_blocks = $block_storage->getQuery()
+      ->accessCheck(FALSE)
+      ->condition('theme', $base_theme)
+      ->execute();
+    // Installing a hidden base theme does not copy the blocks from the default
+    // theme.
+    $this->assertEmpty($new_blocks);
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Plugin/migrate/source/BlockTest.php

@@ -0,0 +1,129 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Plugin\migrate\source;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+/**
+ * Tests block source plugin.
+ *
+ * @covers \Drupal\block\Plugin\migrate\source\Block
+ * @group block
+ */
+class BlockTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function providerSource() {
+    $tests = [];
+
+    // The source data.
+    $tests[0]['source_data']['blocks'] = [
+      [
+        'bid' => 1,
+        'module' => 'block',
+        'delta' => '1',
+        'theme' => 'garland',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'left',
+        'visibility' => 0,
+        'pages' => '',
+        'title' => 'Test Title 01',
+        'cache' => -1,
+      ],
+      [
+        'bid' => 2,
+        'module' => 'block',
+        'delta' => '2',
+        'theme' => 'garland',
+        'status' => 1,
+        'weight' => 5,
+        'region' => 'right',
+        'visibility' => 0,
+        'pages' => '<front>',
+        'title' => 'Test Title 02',
+        'cache' => -1,
+      ],
+    ];
+    $tests[0]['source_data']['blocks_roles'] = [
+      [
+        'module' => 'block',
+        'delta' => 1,
+        'rid' => 2,
+      ],
+      [
+        'module' => 'block',
+        'delta' => 2,
+        'rid' => 2,
+      ],
+      [
+        'module' => 'block',
+        'delta' => 2,
+        'rid' => 100,
+      ],
+    ];
+    $tests[0]['source_data']['role'] = [
+      [
+        'rid' => 2,
+        'name' => 'authenticated user',
+      ],
+    ];
+    $tests[0]['source_data']['system'] = [
+      [
+        'filename' => 'modules/system/system.module',
+        'name' => 'system',
+        'type' => 'module',
+        'owner' => '',
+        'status' => '1',
+        'throttle' => '0',
+        'bootstrap' => '0',
+        'schema_version' => '6055',
+        'weight' => '0',
+        'info' => 'a:0:{}',
+      ],
+    ];
+
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'bid' => 1,
+        'module' => 'block',
+        'delta' => '1',
+        'theme' => 'garland',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'left',
+        'visibility' => 0,
+        'pages' => '',
+        'title' => 'Test Title 01',
+        'cache' => -1,
+        'roles' => [2],
+      ],
+      [
+        'bid' => 2,
+        'module' => 'block',
+        'delta' => '2',
+        'theme' => 'garland',
+        'status' => 1,
+        'weight' => 5,
+        'region' => 'right',
+        'visibility' => 0,
+        'pages' => '<front>',
+        'title' => 'Test Title 02',
+        'cache' => -1,
+        'roles' => [2],
+      ],
+    ];
+    return $tests;
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Plugin/migrate/source/d6/BlockTranslationTest.php

@@ -0,0 +1,81 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Plugin\migrate\source\d6;
+
+use Drupal\Tests\block\Kernel\Plugin\migrate\source\BlockTest;
+
+/**
+ * Tests i18n block source plugin.
+ *
+ * @covers \Drupal\block\Plugin\migrate\source\d6\BlockTranslation
+ *
+ * @group content_translation
+ */
+class BlockTranslationTest extends BlockTest {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function providerSource() {
+    // Test data is the same as BlockTest, but with the addition of i18n_blocks.
+    $tests = parent::providerSource();
+
+    // The source data.
+    $tests[0]['source_data']['i18n_blocks'] = [
+      [
+        'ibid' => 1,
+        'module' => 'block',
+        'delta' => '1',
+        'type' => 0,
+        'language' => 'fr',
+      ],
+      [
+        'ibid' => 2,
+        'module' => 'block',
+        'delta' => '2',
+        'type' => 0,
+        'language' => 'zu',
+      ],
+    ];
+    $tests[0]['source_data']['variables'] = [
+      [
+        'name' => 'default_theme',
+        'value' => 's:7:"garland";',
+      ],
+    ];
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'bid' => 1,
+        'module' => 'block',
+        'delta' => '1',
+        'title' => 'Test Title 01',
+        'ibid' => 1,
+        'type' => '0',
+        'language' => 'fr',
+        'default_theme' => 'Garland',
+      ],
+      [
+        'bid' => 2,
+        'module' => 'block',
+        'delta' => '2',
+        'theme' => 'garland',
+        'title' => 'Test Title 02',
+        'ibid' => 2,
+        'type' => '0',
+        'language' => 'zu',
+        'default_theme' => 'Garland',
+      ],
+    ];
+
+    return $tests;
+  }
+
+}

web/core/modules/block/tests/src/Kernel/Plugin/migrate/source/d7/BlockTranslationTest.php

@@ -0,0 +1,190 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Kernel\Plugin\migrate\source\d7;
+
+use Drupal\Tests\migrate\Kernel\MigrateSqlSourceTestBase;
+
+// cspell:ignore objectid objectindex plid textgroup
+
+/**
+ * Tests i18n block source plugin.
+ *
+ * @covers \Drupal\block\Plugin\migrate\source\d7\BlockTranslation
+ *
+ * @group content_translation
+ */
+class BlockTranslationTest extends MigrateSqlSourceTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected static $modules = ['block', 'migrate_drupal'];
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function providerSource() {
+
+    // The source data.
+    $tests[0]['source_data']['block'] = [
+      [
+        'bid' => 1,
+        'module' => 'system',
+        'delta' => 'main',
+        'theme' => 'bartik',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'content',
+        'custom' => '0',
+        'visibility' => 0,
+        'pages' => '',
+        'title' => '',
+        'cache' => -1,
+        'i18n_mode' => 1,
+      ],
+      [
+        'bid' => 2,
+        'module' => 'system',
+        'delta' => 'navigation',
+        'theme' => 'bartik',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'sidebar_first',
+        'custom' => '0',
+        'visibility' => 0,
+        'pages' => '',
+        'title' => 'Navigation',
+        'cache' => -1,
+        'i18n_mode' => 1,
+      ],
+    ];
+    $tests[0]['source_data']['block_role'] = [
+      [
+        'module' => 'block',
+        'delta' => 1,
+        'rid' => 2,
+      ],
+      [
+        'module' => 'block',
+        'delta' => 2,
+        'rid' => 2,
+      ],
+      [
+        'module' => 'block',
+        'delta' => 2,
+        'rid' => 100,
+      ],
+    ];
+    $tests[0]['source_data']['i18n_string'] = [
+      [
+        'lid' => 1,
+        'textgroup' => 'block',
+        'context' => '1',
+        'objectid' => 'navigation',
+        'type' => 'system',
+        'property' => 'title',
+        'objectindex' => 0,
+        'format' => '',
+      ],
+      [
+        'lid' => 2,
+        'textgroup' => 'block',
+        'context' => '1',
+        'objectid' => 'main',
+        'type' => 'system',
+        'property' => 'title',
+        'objectindex' => 0,
+        'format' => '',
+      ],
+    ];
+
+    $tests[0]['source_data']['locales_target'] = [
+      [
+        'lid' => 1,
+        'translation' => 'fr - Navigation',
+        'language' => 'fr',
+        'plid' => 0,
+        'plural' => 0,
+        'i18n_status' => 0,
+      ],
+    ];
+    $tests[0]['source_data']['role'] = [
+      [
+        'rid' => 2,
+        'name' => 'authenticated user',
+      ],
+    ];
+    $tests[0]['source_data']['system'] = [
+      [
+        'filename' => 'modules/system/system.module',
+        'name' => 'system',
+        'type' => 'module',
+        'owner' => '',
+        'status' => '1',
+        'throttle' => '0',
+        'bootstrap' => '0',
+        'schema_version' => '7055',
+        'weight' => '0',
+        'info' => 'a:0:{}',
+      ],
+    ];
+    // The expected results.
+    $tests[0]['expected_data'] = [
+      [
+        'bid' => 2,
+        'module' => 'system',
+        'delta' => 'navigation',
+        'theme' => 'bartik',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'sidebar_first',
+        'custom' => '0',
+        'visibility' => 0,
+        'pages' => '',
+        'title' => 'Navigation',
+        'cache' => -1,
+        'i18n_mode' => 1,
+        'lid' => 1,
+        'translation' => 'fr - Navigation',
+        'language' => 'fr',
+        'plid' => 0,
+        'plural' => 0,
+        'i18n_status' => 0,
+      ],
+    ];
+
+    // Change the name of the locale_target i18n status field.
+    $tests[1] = $tests[0];
+    foreach ($tests[1]['source_data']['locales_target'] as &$lt) {
+      $lt['status'] = $lt['i18n_status'];
+      unset($lt['i18n_status']);
+    }
+    $tests[1]['expected_data'] = [
+      [
+        'bid' => 2,
+        'module' => 'system',
+        'delta' => 'navigation',
+        'theme' => 'bartik',
+        'status' => 1,
+        'weight' => 0,
+        'region' => 'sidebar_first',
+        'custom' => '0',
+        'visibility' => 0,
+        'pages' => '',
+        'title' => 'Navigation',
+        'cache' => -1,
+        'i18n_mode' => 1,
+        'lid' => 1,
+        'translation' => 'fr - Navigation',
+        'language' => 'fr',
+        'plid' => 0,
+        'plural' => 0,
+        'i18n_status' => 0,
+      ],
+    ];
+    return $tests;
+  }
+
+}

web/core/modules/block/tests/src/Traits/BlockCreationTrait.php

@@ -0,0 +1,68 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Traits;
+
+use Drupal\block\Entity\Block;
+
+/**
+ * Provides methods to create and place block with default settings.
+ *
+ * This trait is meant to be used only by test classes.
+ */
+trait BlockCreationTrait {
+
+  /**
+   * Creates a block instance based on default settings.
+   *
+   * @param string $plugin_id
+   *   The plugin ID of the block type for this block instance.
+   * @param array $settings
+   *   (optional) An associative array of settings for the block entity.
+   *   Override the defaults by specifying the key and value in the array, for
+   *   example:
+   *   @code
+   *     $this->drupalPlaceBlock('system_powered_by_block', [
+   *       'label' => 'Hello, world!',
+   *     ]);
+   *   @endcode
+   *   The following defaults are provided:
+   *   - label: Random string.
+   *   - id: Random string.
+   *   - region: 'content'.
+   *   - theme: The default theme.
+   *   - visibility: Empty array (block will be visible on all pages).
+   *
+   * @return \Drupal\block\Entity\Block
+   *   The block entity.
+   *
+   * @todo Add support for creating content block instances.
+   */
+  protected function placeBlock($plugin_id, array $settings = []) {
+    $config = \Drupal::configFactory();
+    $settings += [
+      'plugin' => $plugin_id,
+      'region' => 'content',
+      'id' => $this->randomMachineName(8),
+      'theme' => $config->get('system.theme')->get('default'),
+      'label' => $this->randomMachineName(8),
+      'visibility' => [],
+      'weight' => 0,
+    ];
+    $values = [];
+    foreach (['region', 'id', 'theme', 'plugin', 'weight', 'visibility'] as $key) {
+      $values[$key] = $settings[$key];
+      // Remove extra values that do not belong in the settings array.
+      unset($settings[$key]);
+    }
+    foreach ($values['visibility'] as $id => $visibility) {
+      $values['visibility'][$id]['id'] = $id;
+    }
+    $values['settings'] = $settings;
+    $block = Block::create($values);
+    $block->save();
+    return $block;
+  }
+
+}

web/core/modules/block/tests/src/Unit/BlockConfigEntityUnitTest.php

@@ -0,0 +1,131 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit;
+
+use Drupal\Core\DependencyInjection\ContainerBuilder;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\Core\Extension\ThemeHandlerInterface;
+use Drupal\Tests\Core\Plugin\Fixtures\TestConfigurablePlugin;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\block\Entity\Block
+ * @group block
+ */
+class BlockConfigEntityUnitTest extends UnitTestCase {
+
+  /**
+   * The entity type used for testing.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $entityType;
+
+  /**
+   * The entity type manager used for testing.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The ID of the type of the entity under test.
+   *
+   * @var string
+   */
+  protected $entityTypeId;
+
+  /**
+   * The UUID generator used for testing.
+   *
+   * @var \Drupal\Component\Uuid\UuidInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $uuid;
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface|\Prophecy\Prophecy\ProphecyInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface|\Prophecy\Prophecy\ProphecyInterface
+   */
+  protected $themeHandler;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->entityTypeId = $this->randomMachineName();
+
+    $this->entityType = $this->createMock('\Drupal\Core\Entity\EntityTypeInterface');
+    $this->entityType->expects($this->any())
+      ->method('getProvider')
+      ->willReturn('block');
+
+    $this->entityTypeManager = $this->createMock(EntityTypeManagerInterface::class);
+    $this->entityTypeManager->expects($this->any())
+      ->method('getDefinition')
+      ->with($this->entityTypeId)
+      ->willReturn($this->entityType);
+
+    $this->uuid = $this->createMock('\Drupal\Component\Uuid\UuidInterface');
+
+    $this->moduleHandler = $this->prophesize(ModuleHandlerInterface::class);
+    $this->themeHandler = $this->prophesize(ThemeHandlerInterface::class);
+
+    $container = new ContainerBuilder();
+    $container->set('entity_type.manager', $this->entityTypeManager);
+    $container->set('module_handler', $this->moduleHandler->reveal());
+    $container->set('theme_handler', $this->themeHandler->reveal());
+    $container->set('uuid', $this->uuid);
+    \Drupal::setContainer($container);
+  }
+
+  /**
+   * @covers ::calculateDependencies
+   */
+  public function testCalculateDependencies(): void {
+    $this->themeHandler->themeExists('stark')->willReturn(TRUE);
+    $values = ['theme' => 'stark'];
+    // Mock the entity under test so that we can mock getPluginCollections().
+    $entity = $this->getMockBuilder('\Drupal\block\Entity\Block')
+      ->setConstructorArgs([$values, $this->entityTypeId])
+      ->onlyMethods(['getPluginCollections'])
+      ->getMock();
+    // Create a configurable plugin that would add a dependency.
+    $instance_id = $this->randomMachineName();
+    $this->moduleHandler->moduleExists('test')->willReturn(TRUE);
+    $instance = new TestConfigurablePlugin([], $instance_id, ['provider' => 'test']);
+
+    // Create a plugin collection to contain the instance.
+    $plugin_collection = $this->getMockBuilder('\Drupal\Core\Plugin\DefaultLazyPluginCollection')
+      ->disableOriginalConstructor()
+      ->onlyMethods(['get'])
+      ->getMock();
+    $plugin_collection->expects($this->atLeastOnce())
+      ->method('get')
+      ->with($instance_id)
+      ->willReturn($instance);
+    $plugin_collection->addInstanceId($instance_id);
+
+    // Return the mocked plugin collection.
+    $entity->expects($this->once())
+      ->method('getPluginCollections')
+      ->willReturn([$plugin_collection]);
+
+    $dependencies = $entity->calculateDependencies()->getDependencies();
+    $this->assertContains('test', $dependencies['module']);
+    $this->assertContains('stark', $dependencies['theme']);
+  }
+
+}

web/core/modules/block/tests/src/Unit/BlockFormTest.php

@@ -0,0 +1,184 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit;
+
+use Drupal\block\BlockForm;
+use Drupal\block\BlockRepository;
+use Drupal\block\Entity\Block;
+use Drupal\Core\Block\BlockBase;
+use Drupal\Core\Plugin\PluginFormFactoryInterface;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\block\BlockForm
+ * @group block
+ */
+class BlockFormTest extends UnitTestCase {
+
+  /**
+   * The condition plugin manager.
+   *
+   * @var \Drupal\Core\Executable\ExecutableManagerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $conditionManager;
+
+  /**
+   * The block storage.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $storage;
+
+  /**
+   * The language manager service.
+   *
+   * @var \Drupal\Core\Language\LanguageManagerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $language;
+
+  /**
+   * The theme handler.
+   *
+   * @var \Drupal\Core\Extension\ThemeHandlerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $themeHandler;
+
+  /**
+   * The theme manager service.
+   *
+   * @var \Drupal\Core\Theme\ThemeManagerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $themeManager;
+
+  /**
+   * The entity type manager.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManagerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The mocked context handler.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextHandlerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $contextHandler;
+
+  /**
+   * The mocked context repository.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextRepositoryInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $contextRepository;
+
+  /**
+   * The plugin form manager.
+   *
+   * @var \Drupal\Core\Plugin\PluginFormFactoryInterface|\Prophecy\Prophecy\ProphecyInterface
+   */
+  protected $pluginFormFactory;
+
+  /**
+   * The block repository.
+   *
+   * @var \Drupal\block\BlockRepositoryInterface
+   */
+  protected $blockRepository;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $this->conditionManager = $this->createMock('Drupal\Core\Executable\ExecutableManagerInterface');
+    $this->language = $this->createMock('Drupal\Core\Language\LanguageManagerInterface');
+    $this->contextRepository = $this->createMock('Drupal\Core\Plugin\Context\ContextRepositoryInterface');
+
+    $this->entityTypeManager = $this->createMock('Drupal\Core\Entity\EntityTypeManagerInterface');
+    $this->storage = $this->createMock('Drupal\Core\Config\Entity\ConfigEntityStorageInterface');
+    $this->themeHandler = $this->createMock('Drupal\Core\Extension\ThemeHandlerInterface');
+    $this->entityTypeManager->expects($this->any())
+      ->method('getStorage')
+      ->willReturn($this->storage);
+
+    $this->pluginFormFactory = $this->prophesize(PluginFormFactoryInterface::class);
+
+    $this->themeManager = $this->createMock('\Drupal\Core\Theme\ThemeManagerInterface');
+    $this->contextHandler = $this->createMock('Drupal\Core\Plugin\Context\ContextHandlerInterface');
+    $this->blockRepository = new BlockRepository($this->entityTypeManager, $this->themeManager, $this->contextHandler);
+  }
+
+  /**
+   * Mocks a block with a block plugin.
+   *
+   * @param string $machine_name
+   *   The machine name of the block plugin.
+   *
+   * @return \Drupal\block\BlockInterface|\PHPUnit\Framework\MockObject\MockObject
+   *   The mocked block.
+   */
+  protected function getBlockMockWithMachineName($machine_name) {
+    $plugin = $this->getMockBuilder(BlockBase::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $plugin->expects($this->any())
+      ->method('getMachineNameSuggestion')
+      ->willReturn($machine_name);
+
+    $block = $this->getMockBuilder(Block::class)
+      ->disableOriginalConstructor()
+      ->getMock();
+    $block->expects($this->any())
+      ->method('getPlugin')
+      ->willReturn($plugin);
+    return $block;
+  }
+
+  /**
+   * Tests the unique machine name generator.
+   *
+   * @see \Drupal\block\BlockForm::getUniqueMachineName()
+   */
+  public function testGetUniqueMachineName(): void {
+    $blocks = [];
+
+    $blocks['test'] = $this->getBlockMockWithMachineName('test');
+    $blocks['other_test'] = $this->getBlockMockWithMachineName('other_test');
+    $blocks['other_test_1'] = $this->getBlockMockWithMachineName('other_test');
+    $blocks['other_test_2'] = $this->getBlockMockWithMachineName('other_test');
+
+    $query = $this->createMock('Drupal\Core\Entity\Query\QueryInterface');
+    $query->expects($this->exactly(5))
+      ->method('condition')
+      ->willReturn($query);
+
+    $query->expects($this->exactly(5))
+      ->method('execute')
+      ->willReturn(['test', 'other_test', 'other_test_1', 'other_test_2']);
+
+    $this->storage->expects($this->exactly(5))
+      ->method('getQuery')
+      ->willReturn($query);
+
+    $block_form_controller = new BlockForm($this->entityTypeManager, $this->conditionManager, $this->contextRepository, $this->language, $this->themeHandler, $this->pluginFormFactory->reveal(), $this->blockRepository);
+
+    // Ensure that the block with just one other instance gets
+    // the next available name suggestion.
+    $this->assertEquals('test_2', $block_form_controller->getUniqueMachineName($blocks['test']));
+
+    // Ensure that the block with already three instances (_0, _1, _2) gets the
+    // 4th available name.
+    $this->assertEquals('other_test_3', $block_form_controller->getUniqueMachineName($blocks['other_test']));
+    $this->assertEquals('other_test_3', $block_form_controller->getUniqueMachineName($blocks['other_test_1']));
+    $this->assertEquals('other_test_3', $block_form_controller->getUniqueMachineName($blocks['other_test_2']));
+
+    // Ensure that a block without an instance yet gets the suggestion as
+    // unique machine name.
+    $last_block = $this->getBlockMockWithMachineName('last_test');
+    $this->assertEquals('last_test', $block_form_controller->getUniqueMachineName($last_block));
+  }
+
+}

web/core/modules/block/tests/src/Unit/BlockRepositoryTest.php

@@ -0,0 +1,199 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit;
+
+use Drupal\block\BlockRepository;
+use Drupal\Core\Access\AccessResult;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\block\BlockRepository
+ * @group block
+ */
+class BlockRepositoryTest extends UnitTestCase {
+
+  /**
+   * The block repository.
+   *
+   * @var \Drupal\block\BlockRepository
+   */
+  protected $blockRepository;
+
+  /**
+   * The block storage or a mock.
+   *
+   * @var \Drupal\Core\Entity\EntityStorageInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $blockStorage;
+
+  /**
+   * The theme for the test.
+   *
+   * @var string
+   */
+  protected $theme;
+
+  /**
+   * The context handler of a mock.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextHandlerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $contextHandler;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $active_theme = $this->getMockBuilder('Drupal\Core\Theme\ActiveTheme')
+      ->disableOriginalConstructor()
+      ->getMock();
+    $this->theme = $this->randomMachineName();
+    $active_theme->expects($this->atLeastOnce())
+      ->method('getName')
+      ->willReturn($this->theme);
+    $active_theme->expects($this->atLeastOnce())
+      ->method('getRegions')
+      ->willReturn([
+        'top',
+        'center',
+        'bottom',
+      ]);
+
+    $theme_manager = $this->createMock('Drupal\Core\Theme\ThemeManagerInterface');
+    $theme_manager->expects($this->atLeastOnce())
+      ->method('getActiveTheme')
+      ->willReturn($active_theme);
+
+    $this->contextHandler = $this->createMock('Drupal\Core\Plugin\Context\ContextHandlerInterface');
+    $this->blockStorage = $this->createMock('Drupal\Core\Entity\EntityStorageInterface');
+    /** @var \Drupal\Core\Entity\EntityTypeManagerInterface|\PHPUnit\Framework\MockObject\MockObject $entity_type_manager */
+    $entity_type_manager = $this->createMock(EntityTypeManagerInterface::class);
+    $entity_type_manager->expects($this->any())
+      ->method('getStorage')
+      ->willReturn($this->blockStorage);
+
+    $this->blockRepository = new BlockRepository($entity_type_manager, $theme_manager, $this->contextHandler);
+  }
+
+  /**
+   * Tests the retrieval of block entities.
+   *
+   * @covers ::getVisibleBlocksPerRegion
+   *
+   * @dataProvider providerBlocksConfig
+   */
+  public function testGetVisibleBlocksPerRegion(array $blocks_config, array $expected_blocks): void {
+    $blocks = [];
+    foreach ($blocks_config as $block_id => $block_config) {
+      $block = $this->createMock('Drupal\block\BlockInterface');
+      $block->expects($this->once())
+        ->method('access')
+        ->willReturn($block_config[0]);
+      $block->expects($block_config[0] ? $this->atLeastOnce() : $this->never())
+        ->method('getRegion')
+        ->willReturn($block_config[1]);
+      $block->expects($this->any())
+        ->method('label')
+        ->willReturn($block_id);
+      $block->expects($this->any())
+        ->method('getWeight')
+        ->willReturn($block_config[2]);
+      $blocks[$block_id] = $block;
+    }
+
+    $this->blockStorage->expects($this->once())
+      ->method('loadByProperties')
+      ->with(['theme' => $this->theme])
+      ->willReturn($blocks);
+    $result = [];
+    $cacheable_metadata = [];
+    foreach ($this->blockRepository->getVisibleBlocksPerRegion($cacheable_metadata) as $region => $resulting_blocks) {
+      $result[$region] = [];
+      foreach ($resulting_blocks as $plugin_id => $block) {
+        $result[$region][] = $plugin_id;
+      }
+    }
+    $this->assertEquals($expected_blocks, $result);
+  }
+
+  /**
+   * Provides data to testGetVisibleBlocksPerRegion().
+   */
+  public static function providerBlocksConfig() {
+    $blocks_config = [
+      'block1' => [
+        AccessResult::allowed(), 'top', 0,
+      ],
+      // Test a block without access.
+      'block2' => [
+        AccessResult::forbidden(), 'bottom', 0,
+      ],
+      // Test some blocks in the same region with specific weight.
+      'block4' => [
+        AccessResult::allowed(), 'bottom', 5,
+      ],
+      'block3' => [
+        AccessResult::allowed(), 'bottom', 5,
+      ],
+      'block5' => [
+        AccessResult::allowed(), 'bottom', -5,
+      ],
+    ];
+
+    $test_cases = [];
+    $test_cases[] = [$blocks_config,
+      [
+        'top' => ['block1'],
+        'center' => [],
+        'bottom' => ['block5', 'block3', 'block4'],
+      ],
+    ];
+    return $test_cases;
+  }
+
+  /**
+   * Tests the retrieval of block entities that are context-aware.
+   *
+   * @covers ::getVisibleBlocksPerRegion
+   */
+  public function testGetVisibleBlocksPerRegionWithContext(): void {
+    $block = $this->createMock('Drupal\block\BlockInterface');
+    $block->expects($this->once())
+      ->method('access')
+      ->willReturn(AccessResult::allowed()->addCacheTags(['config:block.block.block_id']));
+    $block->expects($this->once())
+      ->method('getRegion')
+      ->willReturn('top');
+    $blocks['block_id'] = $block;
+
+    $this->blockStorage->expects($this->once())
+      ->method('loadByProperties')
+      ->with(['theme' => $this->theme])
+      ->willReturn($blocks);
+    $result = [];
+    $cacheable_metadata = [];
+    foreach ($this->blockRepository->getVisibleBlocksPerRegion($cacheable_metadata) as $region => $resulting_blocks) {
+      $result[$region] = [];
+      foreach ($resulting_blocks as $plugin_id => $block) {
+        $result[$region][] = $plugin_id;
+      }
+    }
+    $expected = [
+      'top' => [
+        'block_id',
+      ],
+      'center' => [],
+      'bottom' => [],
+    ];
+    $this->assertSame($expected, $result);
+
+    // Assert that the cacheable metadata from the block access results was
+    // collected.
+    $this->assertEquals(['config:block.block.block_id'], $cacheable_metadata['top']->getCacheTags());
+  }
+
+}

web/core/modules/block/tests/src/Unit/CategoryAutocompleteTest.php

@@ -0,0 +1,94 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit;
+
+use Drupal\Component\Utility\Html;
+use Drupal\block\Controller\CategoryAutocompleteController;
+use Drupal\Tests\UnitTestCase;
+use Symfony\Component\HttpFoundation\Request;
+
+/**
+ * @coversDefaultClass \Drupal\block\Controller\CategoryAutocompleteController
+ * @group block
+ */
+class CategoryAutocompleteTest extends UnitTestCase {
+
+  /**
+   * The autocomplete controller.
+   *
+   * @var \Drupal\block\Controller\CategoryAutocompleteController
+   */
+  protected $autocompleteController;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+
+    $block_manager = $this->createMock('Drupal\Core\Block\BlockManagerInterface');
+    $block_manager->expects($this->any())
+      ->method('getCategories')
+      ->willReturn(['Comment', 'Node', 'None & Such', 'User']);
+
+    $this->autocompleteController = new CategoryAutocompleteController($block_manager);
+  }
+
+  /**
+   * Tests the autocomplete method.
+   *
+   * @param string $string
+   *   The string entered into the autocomplete.
+   * @param array $suggestions
+   *   The array of expected suggestions.
+   *
+   * @see \Drupal\block\Controller\CategoryAutocompleteController::autocomplete()
+   *
+   * @dataProvider providerTestAutocompleteSuggestions
+   */
+  public function testAutocompleteSuggestions($string, $suggestions): void {
+    $suggestions = array_map(function ($suggestion) {
+      return ['value' => $suggestion, 'label' => Html::escape($suggestion)];
+    }, $suggestions);
+    $result = $this->autocompleteController->autocomplete(new Request(['q' => $string]));
+    $this->assertSame($suggestions, json_decode($result->getContent(), TRUE));
+  }
+
+  /**
+   * Data provider for testAutocompleteSuggestions().
+   *
+   * @return array
+   *   An array of test cases, each containing an input string and
+   *   expected autocomplete suggestions.
+   */
+  public static function providerTestAutocompleteSuggestions() {
+    $test_parameters = [];
+    $test_parameters[] = [
+      'string' => 'Com',
+      'suggestions' => [
+        'Comment',
+      ],
+    ];
+    $test_parameters[] = [
+      'string' => 'No',
+      'suggestions' => [
+        'Node',
+        'None & Such',
+      ],
+    ];
+    $test_parameters[] = [
+      'string' => 'us',
+      'suggestions' => [
+        'User',
+      ],
+    ];
+    $test_parameters[] = [
+      'string' => 'Banana',
+      'suggestions' => [],
+    ];
+    return $test_parameters;
+  }
+
+}

web/core/modules/block/tests/src/Unit/Menu/BlockLocalTasksTest.php

@@ -0,0 +1,111 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit\Menu;
+
+use Drupal\Tests\Core\Menu\LocalTaskIntegrationTestBase;
+use Symfony\Component\DependencyInjection\ContainerBuilder;
+
+/**
+ * Tests block local tasks.
+ *
+ * @group block
+ */
+class BlockLocalTasksTest extends LocalTaskIntegrationTestBase {
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    $this->directoryList = ['block' => 'core/modules/block'];
+    parent::setUp();
+
+    $config_factory = $this->getConfigFactoryStub([
+      'system.theme' => ['default' => 'test_c'],
+    ]);
+
+    $themes = [];
+    $themes['test_a'] = (object) [
+      'status' => 1,
+      'info' => [
+        'name' => 'test_a',
+        'hidden' => TRUE,
+      ],
+    ];
+    $themes['test_b'] = (object) [
+      'status' => 1,
+      'info' => [
+        'name' => 'test_b',
+      ],
+    ];
+    $themes['test_c'] = (object) [
+      'status' => 1,
+      'info' => [
+        'name' => 'test_c',
+      ],
+    ];
+    $theme_handler = $this->createMock('Drupal\Core\Extension\ThemeHandlerInterface');
+    $theme_handler->expects($this->any())
+      ->method('listInfo')
+      ->willReturn($themes);
+    $theme_handler->expects($this->any())
+      ->method('hasUi')
+      ->willReturnMap([
+        ['test_a', FALSE],
+        ['test_b', TRUE],
+        ['test_c', TRUE],
+      ]);
+
+    $container = new ContainerBuilder();
+    $container->set('config.factory', $config_factory);
+    $container->set('theme_handler', $theme_handler);
+    $container->setParameter('app.root', $this->root);
+    \Drupal::setContainer($container);
+  }
+
+  /**
+   * Tests the admin edit local task.
+   */
+  public function testBlockAdminLocalTasks(): void {
+    $this->assertLocalTasks('entity.block.edit_form', [['entity.block.edit_form']]);
+  }
+
+  /**
+   * Tests the block admin display local tasks.
+   *
+   * @dataProvider providerTestBlockAdminDisplay
+   */
+  public function testBlockAdminDisplay($route, $expected): void {
+    $this->assertLocalTasks($route, $expected);
+  }
+
+  /**
+   * Provides a list of routes to test.
+   */
+  public static function providerTestBlockAdminDisplay() {
+    return [
+      [
+        'block.admin_display',
+        [
+          ['block.admin_display'],
+          [
+            'block.admin_display_theme:test_b',
+            'block.admin_display_theme:test_c',
+          ],
+        ],
+      ],
+      [
+        'block.admin_display_theme',
+        [
+          ['block.admin_display'],
+          [
+            'block.admin_display_theme:test_b',
+            'block.admin_display_theme:test_c',
+          ],
+        ],
+      ],
+    ];
+  }
+
+}

web/core/modules/block/tests/src/Unit/Plugin/DisplayVariant/BlockPageVariantTest.php

@@ -0,0 +1,268 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit\Plugin\DisplayVariant;
+
+use Drupal\block\Plugin\DisplayVariant\BlockPageVariant;
+use Drupal\Core\Cache\CacheableMetadata;
+use Drupal\Core\DependencyInjection\Container;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
+ * @group block
+ */
+class BlockPageVariantTest extends UnitTestCase {
+
+  /**
+   * The block repository.
+   *
+   * @var \Drupal\block\BlockRepositoryInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $blockRepository;
+
+  /**
+   * The block view builder.
+   *
+   * @var \Drupal\Core\Entity\EntityViewBuilderInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $blockViewBuilder;
+
+  /**
+   * The plugin context handler.
+   *
+   * @var \Drupal\Core\Plugin\Context\ContextHandlerInterface|\PHPUnit\Framework\MockObject\MockObject
+   */
+  protected $contextHandler;
+
+  /**
+   * Sets up a display variant plugin for testing.
+   *
+   * @param array $configuration
+   *   An array of plugin configuration.
+   * @param array $definition
+   *   The plugin definition array.
+   *
+   * @return \Drupal\block\Plugin\DisplayVariant\BlockPageVariant
+   *   A test display variant plugin.
+   */
+  public function setUpDisplayVariant($configuration = [], $definition = []) {
+
+    $container = new Container();
+    $cache_context_manager = $this->getMockBuilder('Drupal\Core\Cache\Context\CacheContextsManager')
+      ->disableOriginalConstructor()
+      ->onlyMethods(['assertValidTokens'])
+      ->getMock();
+    $container->set('cache_contexts_manager', $cache_context_manager);
+    $cache_context_manager->expects($this->any())
+      ->method('assertValidTokens')
+      ->willReturn(TRUE);
+    \Drupal::setContainer($container);
+
+    $this->blockRepository = $this->createMock('Drupal\block\BlockRepositoryInterface');
+    $this->blockViewBuilder = $this->createMock('Drupal\Core\Entity\EntityViewBuilderInterface');
+
+    return new BlockPageVariant($configuration, 'test', $definition, $this->blockRepository, $this->blockViewBuilder, ['config:block_list']);
+  }
+
+  /**
+   * Provides data to testBuild().
+   */
+  public static function providerBuild() {
+    $blocks_config = [
+      'block1' => [
+        // region, is main content block, is messages block, is title block
+        'top', FALSE, FALSE, FALSE,
+      ],
+      // Test multiple blocks in the same region.
+      'block2' => [
+        'bottom', FALSE, FALSE, FALSE,
+      ],
+      'block3' => [
+        'bottom', FALSE, FALSE, FALSE,
+      ],
+      // Test a block implementing MainContentBlockPluginInterface.
+      'block4' => [
+        'center', TRUE, FALSE, FALSE,
+      ],
+      // Test a block implementing MessagesBlockPluginInterface.
+      'block5' => [
+        'center', FALSE, TRUE, FALSE,
+      ],
+      // Test a block implementing TitleBlockPluginInterface.
+      'block6' => [
+        'center', FALSE, FALSE, TRUE,
+      ],
+    ];
+
+    $test_cases = [];
+    $test_cases[] = [$blocks_config, 6,
+      [
+        '#cache' => [
+          'tags' => [
+            'config:block_list',
+            'route',
+          ],
+          'contexts' => [],
+          'max-age' => -1,
+        ],
+        'top' => [
+          'block1' => [],
+          '#sorted' => TRUE,
+        ],
+        // The main content was rendered via a block.
+        'center' => [
+          'block4' => [],
+          'block5' => [],
+          'block6' => [],
+          '#sorted' => TRUE,
+        ],
+        'bottom' => [
+          'block2' => [],
+          'block3' => [],
+          '#sorted' => TRUE,
+        ],
+      ],
+    ];
+    unset($blocks_config['block5']);
+    $test_cases[] = [$blocks_config, 5,
+      [
+        '#cache' => [
+          'tags' => [
+            'config:block_list',
+            'route',
+          ],
+          'contexts' => [],
+          'max-age' => -1,
+        ],
+        'top' => [
+          'block1' => [],
+          '#sorted' => TRUE,
+        ],
+        'center' => [
+          'block4' => [],
+          'block6' => [],
+          '#sorted' => TRUE,
+        ],
+        'bottom' => [
+          'block2' => [],
+          'block3' => [],
+          '#sorted' => TRUE,
+        ],
+        // The messages are rendered via the fallback in case there is no block
+        // rendering the main content.
+        'content' => [
+          'messages' => [
+            '#weight' => -1000,
+            '#type' => 'status_messages',
+            '#include_fallback' => TRUE,
+          ],
+        ],
+      ],
+    ];
+    unset($blocks_config['block4']);
+    unset($blocks_config['block6']);
+    $test_cases[] = [$blocks_config, 3,
+      [
+        '#cache' => [
+          'tags' => [
+            'config:block_list',
+            'route',
+          ],
+          'contexts' => [],
+          'max-age' => -1,
+        ],
+        'top' => [
+          'block1' => [],
+          '#sorted' => TRUE,
+        ],
+        'bottom' => [
+          'block2' => [],
+          'block3' => [],
+          '#sorted' => TRUE,
+        ],
+        // The main content & messages are rendered via the fallback in case
+        // there are no blocks rendering them.
+        'content' => [
+          'system_main' => ['#markup' => 'Hello kittens!'],
+          'messages' => [
+            '#weight' => -1000,
+            '#type' => 'status_messages',
+            '#include_fallback' => TRUE,
+          ],
+        ],
+      ],
+    ];
+    return $test_cases;
+  }
+
+  /**
+   * Tests the building of a full page variant.
+   *
+   * @covers ::build
+   *
+   * @dataProvider providerBuild
+   */
+  public function testBuild(array $blocks_config, $visible_block_count, array $expected_render_array): void {
+    $display_variant = $this->setUpDisplayVariant();
+    $display_variant->setMainContent(['#markup' => 'Hello kittens!']);
+
+    $blocks = ['top' => [], 'center' => [], 'bottom' => []];
+    $block_plugin = $this->createMock('Drupal\Core\Block\BlockPluginInterface');
+    $main_content_block_plugin = $this->createMock('Drupal\Core\Block\MainContentBlockPluginInterface');
+    $messages_block_plugin = $this->createMock('Drupal\Core\Block\MessagesBlockPluginInterface');
+    $title_block_plugin = $this->createMock('Drupal\Core\Block\TitleBlockPluginInterface');
+    foreach ($blocks_config as $block_id => $block_config) {
+      $block = $this->createMock('Drupal\block\BlockInterface');
+      $block->expects($this->atLeastOnce())
+        ->method('getPlugin')
+        ->willReturn($block_config[1] ? $main_content_block_plugin : ($block_config[2] ? $messages_block_plugin : ($block_config[3] ? $title_block_plugin : $block_plugin)));
+      $blocks[$block_config[0]][$block_id] = $block;
+    }
+    $this->blockViewBuilder->expects($this->exactly($visible_block_count))
+      ->method('view')
+      ->willReturn([]);
+    $this->blockRepository->expects($this->once())
+      ->method('getVisibleBlocksPerRegion')
+      ->willReturnCallback(function (&$cacheable_metadata) use ($blocks) {
+        $cacheable_metadata['top'] = (new CacheableMetadata())->addCacheTags(['route']);
+        return $blocks;
+      });
+
+    $value = $display_variant->build();
+    $this->assertSame($expected_render_array, $value);
+  }
+
+  /**
+   * Tests the building of a full page variant with no main content set.
+   *
+   * @covers ::build
+   */
+  public function testBuildWithoutMainContent(): void {
+    $display_variant = $this->setUpDisplayVariant();
+    $this->blockRepository->expects($this->once())
+      ->method('getVisibleBlocksPerRegion')
+      ->willReturn([]);
+
+    $expected = [
+      '#cache' => [
+        'tags' => [
+          'config:block_list',
+        ],
+        'contexts' => [],
+        'max-age' => -1,
+      ],
+      'content' => [
+        'system_main' => [],
+        'messages' => [
+          '#weight' => -1000,
+          '#type' => 'status_messages',
+          '#include_fallback' => TRUE,
+        ],
+      ],
+    ];
+    $this->assertSame($expected, $display_variant->build());
+  }
+
+}

web/core/modules/block/tests/src/Unit/Plugin/migrate/process/BlockRegionTest.php

@@ -0,0 +1,76 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit\Plugin\migrate\process;
+
+use Drupal\block\Plugin\migrate\process\BlockRegion;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Row;
+use Drupal\Tests\UnitTestCase;
+
+/**
+ * @coversDefaultClass \Drupal\block\Plugin\migrate\process\BlockRegion
+ * @group block
+ */
+class BlockRegionTest extends UnitTestCase {
+
+  /**
+   * Transforms a value through the block_region plugin.
+   *
+   * @param array $value
+   *   The value to transform.
+   * @param \Drupal\migrate\Row|null $row
+   *   (optional) The mocked row.
+   *
+   * @return array|string
+   *   The transformed value.
+   */
+  protected function transform(array $value, ?Row $row = NULL) {
+    $executable = $this->prophesize(MigrateExecutableInterface::class)->reveal();
+    if (empty($row)) {
+      $row = $this->prophesize(Row::class)->reveal();
+    }
+
+    $configuration = [
+      'map' => [
+        'bartik' => [
+          'bartik' => [
+            'triptych_first' => 'triptych_first',
+            'triptych_middle' => 'triptych_second',
+            'triptych_last' => 'triptych_third',
+          ],
+        ],
+      ],
+      'default_value' => 'content',
+    ];
+
+    $plugin = new BlockRegion($configuration, 'block_region', [], $configuration['map']['bartik']['bartik']);
+    return $plugin->transform($value, $executable, $row, 'foo');
+  }
+
+  /**
+   * Tests transforming a block with the same theme and an existing region.
+   *
+   * If the source and destination themes are identical, the region should only
+   * be passed through if it actually exists in the destination theme.
+   *
+   * @covers ::transform
+   */
+  public function testTransformSameThemeRegionExists(): void {
+    $this->assertSame('triptych_second', $this->transform(['bartik', 'bartik', 'triptych_middle']));
+  }
+
+  /**
+   * Tests transforming a block with the same theme and a non-existent region.
+   *
+   * If the source and destination themes are identical, the region should be
+   * changed to 'content' if it doesn't exist in the destination theme.
+   *
+   * @covers ::transform
+   */
+  public function testTransformSameThemeRegionNotExists(): void {
+    $this->assertSame('content', $this->transform(['bartik', 'bartik', 'footer']));
+  }
+
+}

web/core/modules/block/tests/src/Unit/Plugin/migrate/process/BlockSettingsTest.php

@@ -0,0 +1,100 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit\Plugin\migrate\process;
+
+use Drupal\block\Plugin\migrate\process\BlockSettings;
+use Drupal\Core\Block\BlockManagerInterface;
+use Drupal\Core\Block\BlockPluginInterface;
+use Drupal\migrate\MigrateExecutableInterface;
+use Drupal\migrate\Row;
+use Drupal\Tests\UnitTestCase;
+use Prophecy\Argument;
+
+/**
+ * @coversDefaultClass \Drupal\block\Plugin\migrate\process\BlockSettings
+ * @group block
+ */
+class BlockSettingsTest extends UnitTestCase {
+
+  /**
+   * Tests the blocks settings process plugin.
+   *
+   * @param array $value
+   *   The source value for the plugin.
+   * @param array $expected
+   *   The expected result.
+   *
+   * @covers ::transform
+   *
+   * @dataProvider providerTestTransform
+   */
+  public function testTransform($value, $expected): void {
+    $executable = $this->prophesize(MigrateExecutableInterface::class)
+      ->reveal();
+    $row = $this->prophesize(Row::class)->reveal();
+
+    // The block plugin should be asked to provide default configuration.
+    $expected['default'] = 'value';
+
+    $mock_plugin = $this->prophesize(BlockPluginInterface::class);
+    $mock_plugin->getConfiguration()
+      ->shouldBeCalled()
+      ->willReturn($expected);
+
+    $block_manager = $this->prophesize(BlockManagerInterface::class);
+    $block_manager->createInstance($value[0], Argument::type('array'))
+      ->shouldBeCalled()
+      ->willReturn($mock_plugin->reveal());
+
+    $plugin = new BlockSettings([], 'block_settings', [], $block_manager->reveal());
+    $actual = $plugin->transform($value, $executable, $row, 'foo');
+    $this->assertSame($expected, $actual);
+  }
+
+  /**
+   * Provides data for testTransform.
+   */
+  public static function providerTestTransform() {
+    return [
+      'title set' => [
+        [
+          'custom',
+          0,
+          'foo',
+          'title',
+        ],
+        [
+          'label' => 'title',
+          'label_display' => 'visible',
+        ],
+      ],
+      'title empty' => [
+        [
+          'custom',
+          0,
+          'foo',
+          '',
+        ],
+        [
+          'label' => '',
+          'label_display' => '0',
+        ],
+      ],
+      'title <none>' => [
+        [
+          'custom',
+          0,
+          'foo',
+          '<none>',
+        ],
+        [
+          'label' => '<none>',
+          'label_display' => '0',
+        ],
+      ],
+    ];
+  }
+
+}

web/core/modules/block/tests/src/Unit/Plugin/migrate/process/BlockVisibilityTest.php

@@ -0,0 +1,107 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Drupal\Tests\block\Unit\Plugin\migrate\process;
+
+use Drupal\block\Plugin\migrate\process\BlockVisibility;
+use Drupal\Core\Extension\ModuleHandlerInterface;
+use Drupal\migrate\MigrateLookupInterface;
+use Drupal\migrate\MigrateSkipRowException;
+use Drupal\Tests\migrate\Unit\process\MigrateProcessTestCase;
+
+// cspell:ignore rbaz
+
+/**
+ * Tests the block_visibility process plugin.
+ *
+ * @coversDefaultClass \Drupal\block\Plugin\migrate\process\BlockVisibility
+ * @group block
+ */
+class BlockVisibilityTest extends MigrateProcessTestCase {
+
+  /**
+   * The module handler.
+   *
+   * @var \Drupal\Core\Extension\ModuleHandlerInterface
+   */
+  protected $moduleHandler;
+
+  /**
+   * {@inheritdoc}
+   */
+  protected function setUp(): void {
+    parent::setUp();
+    $this->moduleHandler = $this->prophesize(ModuleHandlerInterface::class);
+    $migrate_lookup = $this->prophesize(MigrateLookupInterface::class);
+    $this->plugin = new BlockVisibility([], 'block_visibility_pages', [], $this->moduleHandler->reveal(), $migrate_lookup->reveal());
+  }
+
+  /**
+   * @covers ::transform
+   */
+  public function testTransformNoData(): void {
+    $transformed_value = $this->plugin->transform([0, '', []], $this->migrateExecutable, $this->row, 'destination_property');
+    $this->assertEmpty($transformed_value);
+  }
+
+  /**
+   * @covers ::transform
+   */
+  public function testTransformSinglePageWithFront(): void {
+    $visibility = $this->plugin->transform([0, '<front>', []], $this->migrateExecutable, $this->row, 'destination_property');
+    $this->assertSame('request_path', $visibility['request_path']['id']);
+    $this->assertTrue($visibility['request_path']['negate']);
+    $this->assertSame('<front>', $visibility['request_path']['pages']);
+  }
+
+  /**
+   * @covers ::transform
+   */
+  public function testTransformMultiplePagesWithFront(): void {
+    $visibility = $this->plugin->transform([1, "foo\n/bar\rbaz\r\n<front>", []], $this->migrateExecutable, $this->row, 'destination_property');
+    $this->assertSame('request_path', $visibility['request_path']['id']);
+    $this->assertFalse($visibility['request_path']['negate']);
+    $this->assertSame("/foo\n/bar\n/baz\n<front>", $visibility['request_path']['pages']);
+  }
+
+  /**
+   * @covers ::transform
+   */
+  public function testTransformPhpEnabled(): void {
+    $this->moduleHandler->moduleExists('php')->willReturn(TRUE);
+    $visibility = $this->plugin->transform([2, '<?php', []], $this->migrateExecutable, $this->row, 'destination_property');
+    $this->assertSame('php', $visibility['php']['id']);
+    $this->assertFalse($visibility['php']['negate']);
+    $this->assertSame('<?php', $visibility['php']['php']);
+  }
+
+  /**
+   * @covers ::transform
+   */
+  public function testTransformPhpDisabled(): void {
+    $this->moduleHandler->moduleExists('php')->willReturn(FALSE);
+    $transformed_value = $this->plugin->transform([2, '<?php', []], $this->migrateExecutable, $this->row, 'destination_property');
+    $this->assertEmpty($transformed_value);
+  }
+
+  /**
+   * @covers ::transform
+   */
+  public function testTransformException(): void {
+    $this->moduleHandler->moduleExists('php')->willReturn(FALSE);
+    $migrate_lookup = $this->prophesize(MigrateLookupInterface::class);
+    $this->row = $this->getMockBuilder('Drupal\migrate\Row')
+      ->disableOriginalConstructor()
+      ->onlyMethods(['getSourceProperty'])
+      ->getMock();
+    $this->row->expects($this->exactly(2))
+      ->method('getSourceProperty')
+      ->willReturnMap([['bid', 99], ['module', 'foobar']]);
+    $this->plugin = new BlockVisibility(['skip_php' => TRUE], 'block_visibility_pages', [], $this->moduleHandler->reveal(), $migrate_lookup->reveal());
+    $this->expectException(MigrateSkipRowException::class);
+    $this->expectExceptionMessage("The block with bid '99' from module 'foobar' will have no PHP or request_path visibility configuration.");
+    $this->plugin->transform([2, '<?php', []], $this->migrateExecutable, $this->row, 'destination_property');
+  }
+
+}