https://bitbucket.org/cherrypy/cherrypy/issue/1234

--- cherrypy/test/test_tools.py
+++ cherrypy/test/test_tools.py
@@ -407,4 +407,4 @@
         sa = cherrypy.lib.cptools.SessionAuth()
         res = sa.login_screen(None, username=unicodestr('nobody'),
             password=unicodestr('anypass'))
-        self.assertIsInstance(res, bytestr)
+        self.assertTrue(isinstance(res, bytestr))