def METHOD_NAME(self):
    countdown = Countdown(5)
    timer_task = mock.MagicMock()
    timer_task.side_effect = countdown.step
    timer = RepeatedTimer(0.1, timer_task, condition=lambda: countdown.counter > 0)
    timer.start()
    # wait for it
    timer.join()
    self.assertEqual(5, timer_task.call_count)