def test_utf8Encoding(self):
        """
        The hostname passed to L{clientFromString} is treated as utf-8 bytes;
        it is then encoded as IDNA when it is passed along to
        L{HostnameEndpoint}, and passed as unicode to L{optionsForClientTLS}.
        """
        reactor = object()
        endpoint = endpoints.clientFromString(
            reactor, b'tls:\xc3\xa9xample.example.com:443'
        )
        self.assertEqual(
            endpoint._wrappedEndpoint._hostBytes,
            b'xn--xample-9ua.example.com'
        )
        connectionCreator = connectionCreatorFromEndpoint(
            reactor, endpoint)
        self.assertEqual(connectionCreator._hostname,
                         u'\xe9xample.example.com')

        The hostname passed to L{clientFromString} is treated as utf-8 bytes;
        it is then encoded as IDNA when it is passed along to
        L{HostnameEndpoint}, and passed as unicode to L{optionsForClientTLS}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_endpoints.py