def test_success(self):
        """
        L{ThreadedResolver.getHostByName} returns a L{Deferred} which fires
        with the value returned by the call to L{socket.gethostbyname} in the
        threadpool of the reactor passed to L{ThreadedResolver.__init__}.
        """
        ip = "10.0.0.17"
        name = "foo.bar.example.com"
        timeout = 30

        reactor = FakeReactor()
        self.addCleanup(reactor._stop)

        lookedUp = []
        resolvedTo = []
        def fakeGetHostByName(name):
            lookedUp.append(name)
            return ip

        self.patch(socket, 'gethostbyname', fakeGetHostByName)

        resolver = ThreadedResolver(reactor)
        d = resolver.getHostByName(name, (timeout,))
        d.addCallback(resolvedTo.append)

        reactor._runThreadCalls()

        self.assertEqual(lookedUp, [name])
        self.assertEqual(resolvedTo, [ip])

        # Make sure that any timeout-related stuff gets cleaned up.
        reactor._clock.advance(timeout + 1)
        self.assertEqual(reactor._clock.calls, [])

        L{ThreadedResolver.getHostByName} returns a L{Deferred} which fires
        with the value returned by the call to L{socket.gethostbyname} in the
        threadpool of the reactor passed to L{ThreadedResolver.__init__}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_base.py