def test_notFoundAddress(self):
        """
        If there is no address information for the hostname passed to
        L{searchFileFor}, L{None} is returned.
        """
        hosts = self.path()
        hosts.setContent(
            b"10.2.3.4 foo.example.com\n")
        self.assertIsNone(searchFileFor(hosts.path, b"bar.example.com"))

        If there is no address information for the hostname passed to
        L{searchFileFor}, L{None} is returned.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/names/test/test_hosts.py