clarify mocking in symfony

Author: dbu

clients/mock-client.rst

@@ -226,6 +226,24 @@ Or pass a callable, and return a response or exception based on the request::
 
 .. hint::
 
-    If you're using the :doc:`/integrations/symfony-bundle`, the mock client is available as a service with ``httplug.client.mock`` id.
+    If you're using the :doc:`/integrations/symfony-bundle`, the mock client is
+    available as a service with ``httplug.client.mock`` id.
+    
+    For functional tests, you can overwrite the http client services with the mock
+    client in the test environment:
+    
+        # config/services_test.yaml
+        services:
+            # overwrite the http clients for mocking
+            httplug.client.my_client:
+                class: Http\Mock\Client
+                public: true
+           
+    This will configure your actual services with the mock client. Setting the service
+    public allows you to fetch the mock client from the container to configure it.
+    
+    Note that if you enable a decorator client, e.g. ``http_methods_client: true``,
+    the mock client will be wrapped as well. As usual, the inner client is available
+    by appending ``.inner`` to the service name, e.g. ``httplug.client.my_client.inner``.
 
 .. include:: includes/further-reading-async.inc