Update to Drupal 8.0.0 beta 14. For more information, see https://drupal.org/node/2544542

core/modules/config/tests/config_test/config_test.module

@@ -10,16 +10,6 @@ use Symfony\Component\HttpFoundation\RedirectResponse;
 
 require_once dirname(__FILE__) . '/config_test.hooks.inc';
 
-/**
- * Loads a ConfigTest object.
- *
- * @param string $id
- *   The ID of the ConfigTest object to load.
- */
-function config_test_load($id) {
-  return entity_load('config_test', $id);
-}
-
 /**
  * Implements hook_cache_flush().
  */

core/modules/config/tests/config_test/src/ConfigTestForm.php

@@ -8,13 +8,41 @@
 namespace Drupal\config_test;
 
 use Drupal\Core\Entity\EntityForm;
+use Drupal\Core\Entity\Query\QueryFactory;
 use Drupal\Core\Form\FormStateInterface;
+use Symfony\Component\DependencyInjection\ContainerInterface;
 
 /**
  * Form controller for the test config edit forms.
  */
 class ConfigTestForm extends EntityForm {
 
+  /**
+   * The entity query.
+   *
+   * @var \Drupal\Core\Entity\Query\QueryFactory
+   */
+  protected $entityQuery;
+
+  /**
+   * Constructs a new ConfigTestForm.
+   *
+   * @param \Drupal\Core\Entity\Query\QueryFactory $entity_query
+   *   The entity query.
+   */
+  public function __construct(QueryFactory $entity_query) {
+    $this->entityQuery = $entity_query;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public static function create(ContainerInterface $container) {
+    return new static(
+      $container->get('entity.query')
+    );
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -33,7 +61,7 @@ class ConfigTestForm extends EntityForm {
       '#default_value' => $entity->id(),
       '#required' => TRUE,
       '#machine_name' => array(
-        'exists' => 'config_test_load',
+        'exists' => [$this, 'exists'],
         'replace_pattern' => '[^a-z0-9_.]+',
       ),
     );
@@ -142,4 +170,25 @@ class ConfigTestForm extends EntityForm {
     $form_state->setRedirectUrl($this->entity->urlInfo('collection'));
   }
 
+  /**
+   * Determines if the entity already exists.
+   *
+   * @param string|int $entity_id
+   *   The entity ID.
+   * @param array $element
+   *   The form element.
+   * @param \Drupal\Core\Form\FormStateInterface $form_state
+   *   The current state of the form.
+   *
+   * @return bool
+   *   TRUE if the entity exists, FALSE otherwise.
+   */
+  public function exists($entity_id, array $element, FormStateInterface $form_state) {
+    /** @var \Drupal\Core\Config\Entity\ConfigEntityInterface $entity */
+    $entity = $form_state->getFormObject()->getEntity();
+    return (bool) $this->entityQuery->get($entity->getEntityTypeId())
+      ->condition($entity->getEntityType()->getKey('id'), $entity_id)
+      ->execute();
+  }
+
 }