trait SolrBackendTrait in Search API Solr 4.x

trait SolrBackendTrait {
  use SolrCommitTrait;

  /**
   * Swap the DB backend for a Solr backend.
   *
   * This function has to be called from the test setUp() function.
   */
  protected function enableSolrServer() {
    $config = '/config/install/search_api.server.solr_search_server' . ('true' === SOLR_CLOUD ? '_cloud' : '') . '.yml';
    $this->server = Server::create(Yaml::parse(file_get_contents(drupal_get_path('module', 'search_api_solr_test') . $config)));
    $this->server
      ->save();
    $this->index
      ->setServer($this->server);
    $this->index
      ->save();
    $index_storage = $this->container
      ->get('entity_type.manager')
      ->getStorage('search_api_index');
    $index_storage
      ->resetCache([
      $this->index
        ->id(),
    ]);
    $this->index = $index_storage
      ->load($this->index
      ->id());
  }

  /**
   * {@inheritdoc}
   */
  protected function indexItems() {
    $index_status = parent::indexItems();
    $this
      ->ensureCommit($this->index);
    return $index_status;
  }

  /**
   * {@inheritdoc}
   */
  protected function tearDown() {
    $this->index
      ->clear();
    $this
      ->ensureCommit($this->index);
    parent::tearDown();
  }

}