def test_authoritativeMessage(self):
        """
        The L{RRHeader} instances created by L{Message} from an authoritative
        message are marked as authoritative.
        """
        buf = BytesIO()
        answer = dns.RRHeader(payload=dns.Record_A('1.2.3.4', ttl=0))
        answer.encode(buf)
        message = dns.Message()
        message.fromStr(
            b'\x01\x00' # Message ID
            # answer bit, opCode nibble, auth bit, trunc bit, recursive bit
            b'\x04'
            # recursion bit, empty bit, authenticData bit,
            # checkingDisabled bit, response code nibble
            b'\x00'
            b'\x00\x00' # number of queries
            b'\x00\x01' # number of answers
            b'\x00\x00' # number of authorities
            b'\x00\x00' # number of additionals
            + buf.getvalue()
            )
        answer.auth = True
        self.assertEqual(message.answers, [answer])
        self.assertTrue(message.answers[0].auth)

        The L{RRHeader} instances created by L{Message} from an authoritative
        message are marked as authoritative.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_dns.py