class TestEntityFormController

class TestEntityFormController extends EntityFormController {

  /**
   * Overrides Drupal\Core\Entity\EntityFormController::form().
   */
  public function form(array $form, array &$form_state, EntityInterface $entity) {
    $form = parent::form($form, $form_state, $entity);
    if (!$entity
      ->isNew()) {
      $form['revision'] = array(
        '#access' => user_access('administer field_test content'),
        '#type' => 'checkbox',
        '#title' => t('Create new revision'),
        '#default_value' => FALSE,
        '#weight' => 100,
      );
    }
    return $form;
  }

  /**
   * Overrides Drupal\Core\Entity\EntityFormController::save().
   */
  public function save(array $form, array &$form_state) {
    $entity = $this
      ->getEntity($form_state);
    $is_new = $entity
      ->isNew();
    $entity
      ->save();
    $message = $is_new ? t('test_entity @id has been created.', array(
      '@id' => $entity
        ->id(),
    )) : t('test_entity @id has been updated.', array(
      '@id' => $entity
        ->id(),
    ));
    drupal_set_message($message);
    if ($entity
      ->id()) {
      $form_state['redirect'] = 'test-entity/manage/' . $entity
        ->id() . '/edit';
    }
    else {

      // Error on save.
      drupal_set_message(t('The entity could not be saved.'), 'error');
      $form_state['rebuild'] = TRUE;
    }
  }

}