Fixed #16987 -- Improved error message for session tests. Thanks jMyles and...

        # removed the key) results in a new key being generated.

        try:

            session = self.backend('1')

            try:

                session.save()

            except AttributeError:

                self.fail("The session object did not save properly.  Middleware may be saving cache items without namespaces.")

            self.assertNotEqual(session.session_key, '1')

            self.assertEqual(session.get('cat'), None)

            session.delete()