'If the response has an xframe_options_exempt attribute set to False
then it still sets the header, but if it\'s set to True then it doesn\'t.'

def test_response_exempt(self):

    with override_settings(X_FRAME_OPTIONS='SAMEORIGIN'):
        response = HttpResponse()
        response.xframe_options_exempt = False
        r = XFrameOptionsMiddleware().process_response(HttpRequest(), response)
        self.assertEqual(r['X-Frame-Options'], 'SAMEORIGIN')
        response = HttpResponse()
        response.xframe_options_exempt = True
        r = XFrameOptionsMiddleware().process_response(HttpRequest(), response)
        self.assertIsNone(r.get('X-Frame-Options'))
