'The callback returns no message on the first call.'

def test_send_cmd_response_has_no_message(self):

    success_msg = 'success'
    request_args = ['arg1', 'arg2', 'arg3']
    response1 = {'success': True, 'msg': None}
    response2 = {'success': True, 'msg': 'success'}
    request_func = mock.Mock(side_effect=[response1, response2])
    self.assertEqual(response2, self.driver._send_cmd(request_func, success_msg, request_args))
