def _timeoutTest(self, onDone, clientFactory):
        """
        Connect the clientFactory, and check the timeout on the request.
        """
        clock = task.Clock()
        client = clientFactory.buildProtocol(
            address.IPv4Address('TCP', 'example.net', 25))
        client.callLater = clock.callLater
        t = StringTransport()
        client.makeConnection(t)
        t.protocol = client
        def check(ign):
            self.assertEqual(clock.seconds(), 0.5)
        d = self.assertFailure(onDone, smtp.SMTPTimeoutError
            ).addCallback(check)
        # The first call should not trigger the timeout
        clock.advance(0.1)
        # But this one should
        clock.advance(0.4)
        return d

        Connect the clientFactory, and check the timeout on the request.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/mail/test/test_smtp.py