def test_stopService(self):
        """
        L{StreamServerEndpointService.stopService} calls C{stopListening} on
        the L{IListeningPort} returned from its endpoint, returns the
        C{Deferred} from stopService, and sets C{running} to C{False}.
        """
        self.svc.privilegedStartService()
        self.fakeServer.startedListening()
        # Ensure running gets set to true
        self.svc.startService()
        result = self.svc.stopService()
        l = []
        result.addCallback(l.append)
        self.assertEqual(len(l), 0)
        self.fakeServer.stoppedListening()
        self.assertEqual(len(l), 1)
        self.assertFalse(self.svc.running)

        L{StreamServerEndpointService.stopService} calls C{stopListening} on
        the L{IListeningPort} returned from its endpoint, returns the
        C{Deferred} from stopService, and sets C{running} to C{False}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/test/test_internet.py