def test_delegationLookupError(self):
        """
        If there is an error resolving the nameserver in a delegation response,
        the L{Deferred} returned by L{Resolver.lookupAddress} fires with that
        error.
        """
        servers = {
            ('1.1.2.3', 53): {
                (b'example.com', A): {
                    'authority': [(b'example.com', Record_NS(b'ns1.example.com'))],
                    },
                (b'ns1.example.com', A): {
                    'rCode': ENAME,
                    },
                },
            }
        resolver = self._getResolver(servers)
        d = resolver.lookupAddress(b'example.com')
        return self.assertFailure(d, DNSNameError)

        If there is an error resolving the nameserver in a delegation response,
        the L{Deferred} returned by L{Resolver.lookupAddress} fires with that
        error.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_rootresolve.py