trait ExampleContentTrait in Search API 8

trait ExampleContentTrait {

  /**
   * The generated test entities, keyed by ID.
   *
   * @var \Drupal\entity_test\Entity\EntityTestMulRevChanged[]
   */
  protected $entities = [];

  /**
   * The Search API item IDs of the generated entities.
   *
   * @var string[]
   */
  protected $ids = [];

  /**
   * Sets up the necessary bundles on the test entity type.
   */
  protected function setUpExampleStructure() {
    entity_test_create_bundle('item', NULL, 'entity_test_mulrev_changed');
    entity_test_create_bundle('article', NULL, 'entity_test_mulrev_changed');
  }

  /**
   * Creates several test entities.
   */
  protected function insertExampleContent() {

    // To test Unicode compliance, include all kind of strange characters here.
    $smiley = json_decode('"\\u1F601"');
    $this
      ->addTestEntity(1, [
      'name' => 'foo bar baz foobaz föö smile' . $smiley,
      'body' => 'test test case Case casE',
      'type' => 'item',
      'keywords' => [
        'Orange',
        'orange',
        'örange',
        'Orange',
        $smiley,
      ],
      'category' => 'item_category',
    ]);
    $this
      ->addTestEntity(2, [
      'name' => 'foo test foobuz',
      'body' => 'bar test casE',
      'type' => 'item',
      'keywords' => [
        'orange',
        'apple',
        'grape',
      ],
      'category' => 'item_category',
    ]);
    $this
      ->addTestEntity(3, [
      'name' => 'bar',
      'body' => 'test foobar Case',
      'type' => 'item',
    ]);
    $this
      ->addTestEntity(4, [
      'name' => 'foo baz',
      'body' => 'test test test',
      'type' => 'article',
      'keywords' => [
        'apple',
        'strawberry',
        'grape',
      ],
      'category' => 'article_category',
      'width' => '1.0',
    ]);
    $this
      ->addTestEntity(5, [
      'name' => 'bar baz',
      'body' => 'foo',
      'type' => 'article',
      'keywords' => [
        'orange',
        'strawberry',
        'grape',
        'banana',
      ],
      'category' => 'article_category',
      'width' => '2.0',
    ]);
    $count = \Drupal::entityQuery('entity_test_mulrev_changed')
      ->accessCheck(FALSE)
      ->count()
      ->execute();
    $this
      ->assertEquals(5, $count, "{$count} items inserted.");
  }

  /**
   * Creates and saves a test entity with the given values.
   *
   * @param int $id
   *   The entity's ID.
   * @param array $values
   *   The entity's property values.
   *
   * @return \Drupal\entity_test\Entity\EntityTestMulRevChanged
   *   The created entity.
   */
  protected function addTestEntity($id, array $values) {
    $entity_type = 'entity_test_mulrev_changed';
    $storage = \Drupal::entityTypeManager()
      ->getStorage($entity_type);
    $values['id'] = $id;
    $this->entities[$id] = $storage
      ->create($values);
    $this->entities[$id]
      ->save();
    $this->ids[$id] = Utility::createCombinedId("entity:{$entity_type}", "{$id}:en");
    return $this->entities[$id];
  }

  /**
   * Deletes the test entity with the given ID.
   *
   * @param int $id
   *   The entity's ID.
   *
   * @return $this
   */
  protected function removeTestEntity($id) {
    $this->entities[$id]
      ->delete();
    unset($this->entities[$id]);
    return $this;
  }

  /**
   * Indexes all (unindexed) items on the specified index.
   *
   * @param string $index_id
   *   The ID of the index on which items should be indexed.
   *
   * @return int
   *   The number of successfully indexed items.
   */
  protected function indexItems($index_id) {

    /** @var \Drupal\search_api\IndexInterface $index */
    $index = Index::load($index_id);
    return $index
      ->indexItems();
  }

  /**
   * Returns the item IDs for the given entity IDs.
   *
   * @param array $entity_ids
   *   An array of entity IDs.
   *
   * @return string[]
   *   An array of item IDs.
   */
  protected function getItemIds(array $entity_ids) {
    $map = $this->ids;
    $translate_ids = function ($entity_id) use ($map) {
      return $map[$entity_id];
    };
    return array_map($translate_ids, $entity_ids);
  }

}