    def test_challenge(self):
        rc, root, folder, object = self._makeTree()
        response = FauxCookieResponse()
        testURL = 'http://test'
        request = FauxRequest(RESPONSE=response, URL=testURL,
                              ACTUAL_URL=testURL)
        root.REQUEST = request

        helper = self._makeOne().__of__(root)

        helper.challenge(request, response)
        self.assertEqual(response.status, 302)
        self.assertEqual(len(response.headers), 3)
        self.assertTrue(response.headers['Location'].endswith(quote(testURL)))
        self.assertEqual(response.headers['Cache-Control'], 'no-cache')
        self.assertEqual(response.headers['Expires'],
                         'Sat, 01 Jan 2000 00:00:00 GMT')
A web application accepts a user-controlled input that specifies a link to an external site, and uses that link in a Redirect. This simplifies phishing attacks.