def test_debug(self, mock_Rev2Interface): # gets the rev2_interface # gets the bg_poller mock_bg_poller = mock.Mock() rev2.rev2_interface.bg_poller = mock_bg_poller house_code = HouseCode(code='FA-32') house_code.debug() # tells bg_poller to debug itself mock_bg_poller.debug.assert_called_once_with(house_code)