def test_extendedRcodeZero(self):
        """
        Note that EXTENDED-RCODE value 0 indicates that an unextended RCODE is
        in use (values 0 through 15).

        https://tools.ietf.org/html/rfc6891#section-6.1.3
        """
        ednsMessage = self.messageFactory(rCode=15, ednsVersion=0)
        standardMessage = ednsMessage._toMessage()

        self.assertEqual(
            (15, 0),
            (standardMessage.rCode, standardMessage.additional[0].extendedRCODE)
        )

        Note that EXTENDED-RCODE value 0 indicates that an unextended RCODE is
        in use (values 0 through 15).

        https://tools.ietf.org/html/rfc6891#section-6.1.3
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_dns.py