def test_clientConnectionLostWhileStopping(self):
        """
        When a client connection is lost while the service is stopping, the
        protocol stopping deferred is called and the reference to the protocol
        is removed.
        """
        clock = Clock()
        cq, service = self.makeReconnector(clock=clock)
        d = service.stopService()
        cq.constructedProtocols[0].connectionLost(Failure(IndentationError()))
        self.failureResultOf(service.whenConnected(), CancelledError)
        self.assertTrue(d.called)

        When a client connection is lost while the service is stopping, the
        protocol stopping deferred is called and the reference to the protocol
        is removed.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/application/test/test_internet.py