def test_endpointConnectFailure(self):
        """
        If an endpoint tries to connect to a non-listening port it gets
        a C{ConnectError} failure.
        """
        expectedError = error.ConnectError(string="Connection Failed")

        mreactor = RaisingMemoryReactor(connectException=expectedError)

        clientFactory = object()

        ep, ignoredArgs, ignoredDest = self.createClientEndpoint(
            mreactor, clientFactory)

        d = ep.connect(clientFactory)

        receivedExceptions = []

        def checkFailure(f):
            receivedExceptions.append(f.value)

        d.addErrback(checkFailure)

        self.assertEqual(receivedExceptions, [expectedError])

        If an endpoint tries to connect to a non-listening port it gets
        a C{ConnectError} failure.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_endpoints.py