def test_noPreserve(self):
        """
        L{util.InsensitiveDict} does not preserves the case of keys if
        constructed with C{preserve=False}.
        """
        dct = util.InsensitiveDict({'Foo':'bar', 1:2, 'fnz':{1:2}}, preserve=0)
        keys=['foo', 'fnz', 1]
        for x in keys:
            self.assertIn(x, dct.keys())
            self.assertIn((x, dct[x]), dct.items())
        self.assertEqual(len(keys), len(dct))
        del dct[1]
        del dct['foo']
        self.assertEqual(dct.keys(), ['fnz'])

        L{util.InsensitiveDict} does not preserves the case of keys if
        constructed with C{preserve=False}.
        
stackoverflow/venv/lib/python3.6/site-packages/twisted/python/test/test_util.py