class BigPipeInterfacePreviewThemeSuggestionsTest

class BigPipeInterfacePreviewThemeSuggestionsTest extends KernelTestBase {

  /**
   * {@inheritdoc}
   */
  protected static $modules = [
    'block',
    'big_pipe',
    'system',
  ];

  /**
   * The block being tested.
   *
   * @var \Drupal\block\Entity\BlockInterface
   */
  protected $block;

  /**
   * The block storage.
   *
   * @var \Drupal\Core\Config\Entity\ConfigEntityStorageInterface
   */
  protected $controller;

  /**
   * The block view builder.
   *
   * @var \Drupal\block\BlockViewBuilder
   */
  protected $blockViewBuilder;

  /**
   * {@inheritdoc}
   */
  protected function setUp() : void {
    parent::setUp();
    $this->controller = $this->container
      ->get('entity_type.manager')
      ->getStorage('block');
    $this->blockViewBuilder = $this->container
      ->get('entity_type.manager')
      ->getViewBuilder('block');
    $this->container
      ->get('theme_installer')
      ->install([
      'stark',
    ]);
  }

  /**
   * Tests template suggestions from big_pipe_theme_suggestions_big_pipe_interface_preview().
   */
  public function testBigPipeThemeHookSuggestions() {
    $entity = $this->controller
      ->create([
      'id' => 'test_block1',
      'theme' => 'stark',
      'plugin' => 'system_powered_by_block',
    ]);
    $entity
      ->save();

    // Test the rendering of a block.
    $block = Block::load('test_block1');

    // Using the BlockViewBuilder we will be able to get a lovely
    // #lazy_builder callback assigned.
    $build = $this->blockViewBuilder
      ->view($block);
    $variables = [];

    // In turn this is what createBigPipeJsPlaceholder() uses to
    // build the BigPipe JS placeholder render array which is used as input
    // for big_pipe_theme_suggestions_big_pipe_interface_preview().
    $variables['callback'] = $build['#lazy_builder'][0];
    $variables['arguments'] = $build['#lazy_builder'][1];
    $suggestions = big_pipe_theme_suggestions_big_pipe_interface_preview($variables);
    $suggested_id = preg_replace('/[^a-zA-Z0-9]/', '_', $block
      ->id());
    $this
      ->assertSame([
      'big_pipe_interface_preview__block',
      'big_pipe_interface_preview__block__' . $suggested_id,
      'big_pipe_interface_preview__block__full',
    ], $suggestions);
  }

}