def test_missingPIDVariable(self):
        """
        If the I{LISTEN_PID} environment variable is not present, no inherited
        descriptors are reported.
        """
        fakeEnvironment = self.initializeEnvironment(3, os.getpid())
        del fakeEnvironment['LISTEN_PID']
        sddaemon = ListenFDs.fromEnvironment(environ=fakeEnvironment)
        self.assertEqual([], sddaemon.inheritedDescriptors())

        If the I{LISTEN_PID} environment variable is not present, no inherited
        descriptors are reported.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_systemd.py