def _cancelConnectTest(self, connect):
        """
        Helper for implementing a test to verify that cancellation of the
        L{Deferred} returned by one of L{ClientCreator}'s I{connect} methods is
        implemented to cancel the underlying connector.

        @param connect: A function which will be invoked with a L{ClientCreator}
            instance as an argument and which should call one its I{connect}
            methods and return the result.

        @return: A L{Deferred} which fires when the test is complete or fails if
            there is a problem.
        """
        reactor = MemoryReactorClock()
        cc = ClientCreator(reactor, Protocol)
        d = connect(cc)
        connector = reactor.connectors.pop()
        self.assertFalse(connector._disconnected)
        d.cancel()
        self.assertTrue(connector._disconnected)
        return self.assertFailure(d, CancelledError)

        Helper for implementing a test to verify that cancellation of the
        L{Deferred} returned by one of L{ClientCreator}'s I{connect} methods is
        implemented to cancel the underlying connector.

        @param connect: A function which will be invoked with a L{ClientCreator}
            instance as an argument and which should call one its I{connect}
            methods and return the result.

        @return: A L{Deferred} which fires when the test is complete or fails if
            there is a problem.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_protocol.py