def test_delegationLookupEmpty(self):
        """
        If there are no records in the response to a lookup of a delegation
        nameserver, the L{Deferred} returned by L{Resolver.lookupAddress} fires
        with L{ResolverError}.
        """
        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): {
                    },
                },
            }
        resolver = self._getResolver(servers)
        d = resolver.lookupAddress(b'example.com')
        return self.assertFailure(d, ResolverError)

        If there are no records in the response to a lookup of a delegation
        nameserver, the L{Deferred} returned by L{Resolver.lookupAddress} fires
        with L{ResolverError}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_rootresolve.py