'Textbook IDs must begin with a number; try an invalid one'

def test_invalid_id(self):

    self.textbook['id'] = 'xxx'
    resp = self.client.post(self.url, data=json.dumps(self.textbook), content_type='application/json', HTTP_ACCEPT='application/json', HTTP_X_REQUESTED_WITH='XMLHttpRequest')
    self.assertEqual(resp.status_code, 400)
    self.assertNotIn('Location', resp)
