at the end of the day, it was inevitable

tests/UserBundle/Manager/Notification/RecipientFixture.php

@@ -0,0 +1,55 @@
+<?php
+
+namespace Tests\UserBundle\Manager\Notification;
+
+use ApiBundle\Serializer\Metadata\Metadata;
+use UserBundle\Entity\Recipient\AbstractRecipient;
+
+/**
+ * Class NotificationManagerTest
+ * @package UserBundle\Manager\Notification
+ */
+class RecipientFixture extends AbstractRecipient
+{
+
+    /**
+     * RecipientFixture constructor.
+     *
+     * @param string|integer $id Entity id.
+     */
+    public function __construct($id)
+    {
+        parent::__construct();
+        $this->id = $id;
+    }
+
+    /**
+     * Return fqcn of form used for creating this entity.
+     *
+     * @return string
+     */
+    public function getCreateFormClass()
+    {
+        return '';
+    }
+
+    /**
+     * Return fqcn of form used for updating this entity.
+     *
+     * @return string
+     */
+    public function getUpdateFormClass()
+    {
+        return '';
+    }
+
+    /**
+     * Return metadata for current entity.
+     *
+     * @return \ApiBundle\Serializer\Metadata\Metadata
+     */
+    public function getMetadata()
+    {
+        return new Metadata(static::class);
+    }
+}