diff --git a/cookbook/form/unit_testing.rst b/cookbook/form/unit_testing.rst
index 7a9100fda29..944ed25b372 100644
--- a/cookbook/form/unit_testing.rst
+++ b/cookbook/form/unit_testing.rst
@@ -177,18 +177,22 @@ on other extensions. You need add those extensions to the factory object::
     use Symfony\Component\Form\Forms;
     use Symfony\Component\Form\FormBuilder;
     use Symfony\Component\Form\Extension\Validator\Type\FormTypeValidatorExtension;
+    use Symfony\Component\Validator\ConstraintViolationList;
 
     class TestedTypeTest extends TypeTestCase
     {
         protected function setUp()
         {
             parent::setUp();
+            
+            $validator = $this->getMock('\Symfony\Component\Validator\ValidatorInterface');
+            $validator->method('validate')->will($this->returnValue(new ConstraintViolationList()));
 
             $this->factory = Forms::createFormFactoryBuilder()
                 ->addExtensions($this->getExtensions())
                 ->addTypeExtension(
                     new FormTypeValidatorExtension(
-                        $this->getMock('Symfony\Component\Validator\ValidatorInterface')
+                        $validator
                     )
                 )
                 ->addTypeGuesser(