Unused back in.

I've removed it while refactoring but apparently is need there.

Author: UrszulaNeuman

tests/unit_tests/test_dls_barcode/test_camera/test_camera_switch.py

@@ -171,7 +171,7 @@ def test_given_capture_started_from_top_when_capture_is_stopped_then_timeout_is_
     def _create_switch(self):
         return CameraSwitch(self._mock_scanner, self._mock_timeout)
 
-    def _stream_start_side_effect(self):
+    def _stream_start_side_effect(self, unused):
         self._list_of_calls.append(START)
 
     def _stream_stop_side_effect(self):