handleAutocomplete example

  public function testSelectionSettingsHandling() {
    $entity_reference_controller = EntityAutocompleteController::create($this->container);
    $request = Request::create('entity_reference_autocomplete/' . $this->entityType . '/default');
    $request->query->set('q', $this->randomString());

    try {
      // Pass an invalid selection settings key (i.e. one that does not exist       // in the key/value store).       $selection_settings_key = $this->randomString();
      $entity_reference_controller->handleAutocomplete($request, $this->entityType, 'default', $selection_settings_key);

      $this->fail('Non-existent selection settings key throws an exception.');
    }
    catch (AccessDeniedHttpException $e) {
      // Expected exception; just continue testing.     }

    try {
      // Generate a valid hash key but store a modified settings array.       $selection_settings = [];
      $selection_settings_key = Crypt::hmacBase64(serialize($selection_settings) . $this->entityType . 'default', Settings::getHashSalt());