def test_zoneTransferConnectionFails(self):
        """
        A failed AXFR TCP connection errbacks the L{Deferred} returned
        from L{Resolver.lookupZone}.
        """
        resolver = Resolver(servers=[("nameserver.invalid", 53)])
        return self.assertFailure(resolver.lookupZone("impossible.invalid"),
                                  error.DNSLookupError)

        A failed AXFR TCP connection errbacks the L{Deferred} returned
        from L{Resolver.lookupZone}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_names.py