def test_ensureWhenNotImportedDontPrevent(self):
        """
        If the specified modules have never been imported, and import
        prevention is not requested, L{ensureNotImported} has no effect.
        """
        modules = {}
        self.patch(sys, "modules", modules)
        ensureNotImported(["m1", "m2"], "A message.")
        self.assertEqual(modules, {})

        If the specified modules have never been imported, and import
        prevention is not requested, L{ensureNotImported} has no effect.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/internet/test/test_glibbase.py