Fix testing.rst

Author: peter17

testing.rst

@@ -716,6 +716,8 @@ attributes in this token, you can use the ``tokenAttributes`` argument of the
 
 You can also use :class:`Symfony\\Component\\Security\\Core\\User\\InMemoryUser` but you have to define those in the configuration first::
 
+.. code-block:: yaml
+
     // config/packages/security.yaml
     when@test:
         security:
@@ -727,7 +729,6 @@ You can also use :class:`Symfony\\Component\\Security\\Core\\User\\InMemoryUser`
 and then log the user with::
 
     // tests/Controller/ProfileControllerTest.php
-
     use Symfony\Component\Security\Core\User\InMemoryUser;
 
     $client = static::createClient();