def test_secondEnvironment(self):
        """
        Only a single L{Environment} can extract inherited file descriptors.
        """
        fakeEnvironment = self.initializeEnvironment(3, os.getpid())
        first = ListenFDs.fromEnvironment(environ=fakeEnvironment)
        second = ListenFDs.fromEnvironment(environ=fakeEnvironment)
        self.assertEqual(list(range(3, 6)), first.inheritedDescriptors())
        self.assertEqual([], second.inheritedDescriptors())

        Only a single L{Environment} can extract inherited file descriptors.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_systemd.py