'L{server.DNSServerFactory.gotResolver} accepts a L{failure.Failure} and
triggers a response message whose rCode corresponds to the DNS error
contained in the C{Failure}.
@param responseError: The L{Exception} instance which is expected to
trigger C{expectedMessageCode} when it is supplied to
C{gotResolverError}
@type responseError: L{Exception}
@param expectedMessageCode: The C{rCode} which is expected in the
message returned by C{gotResolverError} in response to
C{responseError}.
@type expectedMessageCode: L{int}'

def _assertMessageRcodeForError(self, responseError, expectedMessageCode):

    f = server.DNSServerFactory()
    e = self.assertRaises(RaisingProtocol.WriteMessageArguments, f.gotResolverError, failure.Failure(responseError), protocol=RaisingProtocol(), message=dns.Message(), address=None)
    ((message,), kwargs) = e.args
    self.assertEqual(message.rCode, expectedMessageCode)
