def test_stopServiceBeforeStartService(self):
        """
        Calling L{ClientService.stopService} before
        L{ClientService.startService} returns a L{Deferred} that has
        already fired with L{None}.
        """
        clock = Clock()
        _, service = self.makeReconnector(fireImmediately=False,
                                          startService=False,
                                          clock=clock)
        d = service.stopService()
        self.assertIsNone(self.successResultOf(d))

        Calling L{ClientService.stopService} before
        L{ClientService.startService} returns a L{Deferred} that has
        already fired with L{None}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/test/test_internet.py