def test_domainErrorForNameWithCommonSuffix(self):
        """
        L{FileAuthority} lookup methods errback with L{DomainError} if
        the requested C{name} shares a common suffix with its zone but
        is not actually a descendant of its zone, in terms of its
        sequence of DNS name labels. eg www.the-example.com has
        nothing to do with the zone example.com.
        """
        testDomain = test_domain_com
        testDomainName = b'nonexistent.prefix-' + testDomain.soa[0]
        f = self.failureResultOf(testDomain.lookupAddress(testDomainName))
        self.assertIsInstance(f.value, DomainError)

        L{FileAuthority} lookup methods errback with L{DomainError} if
        the requested C{name} shares a common suffix with its zone but
        is not actually a descendant of its zone, in terms of its
        sequence of DNS name labels. eg www.the-example.com has
        nothing to do with the zone example.com.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_names.py