def test_patch_vary_headers(self):
        headers = ( 
            # Initial vary, new headers, resulting vary.
            (None, ('Accept-Encoding',), 'Accept-Encoding'),
            ('Accept-Encoding', ('accept-encoding',), 'Accept-Encoding'),
            ('Accept-Encoding', ('ACCEPT-ENCODING',), 'Accept-Encoding'),
            ('Cookie', ('Accept-Encoding',), 'Cookie, Accept-Encoding'),
            ('Cookie, Accept-Encoding', ('Accept-Encoding',), 'Cookie, Accept-Encoding'),
            ('Cookie, Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            (None, ('Accept-Encoding', 'COOKIE'), 'Accept-Encoding, COOKIE'),
            ('Cookie,     Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
            ('Cookie    ,     Accept-Encoding', ('Accept-Encoding', 'cookie'), 'Cookie, Accept-Encoding'),
        )
        for initial_vary, newheaders, resulting_vary in headers:
            response = HttpResponse()
            if initial_vary is not None:
                response['Vary'] = initial_vary
            patch_vary_headers(response, newheaders)
            self.assertEqual(response['Vary'], resulting_vary)