def test_UID(self):
        """
        Check UID/GID switches when current effective UID is non-root.
        """
        self._testUIDGIDSwitch(1, 0, 0, 0, [0, 1], [])
        self._testUIDGIDSwitch(1, 0, 1, 0, [], [])
        self._testUIDGIDSwitch(1, 0, 1, 1, [0, 1, 0, 1], [1, 0])
        self._testUIDGIDSwitch(1, 0, 2, 1, [0, 2, 0, 1], [1, 0])

        Check UID/GID switches when current effective UID is non-root.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_util.py