javascript - 解释 "jest.advanceTimersToNextTimer "

Question

我正在学习用 jest 进行测试，我想出了这个方法:jest.advanceTimersToNextTimer。 Jest 的手册说:

Advances all timers by the needed milliseconds so that only the next timeouts/intervals will run. Optionally, you can provide steps, so it will run steps amount of next timeouts/intervals.

但我不清楚它是如何工作的。有人可以解释一下它的作用，并给出一个使用示例吗？谢谢。

Answer 1

使用时jest.advanceTimersToNextTimer(steps) ，您不再需要手动提供毫秒来运行已通过 setTimeout() 或 setInterval() 排队的宏任务。正如医生所说:

Advances all timers by the needed milliseconds so that only the next timeouts/intervals will run.

此外，您可以为 jest.advanceTimersToNextTimer() 方法提供 steps ，以便它将运行 steps 下一个超时/间隔时间。请参阅“应按步骤通过” 测试用例。默认步骤为1，请参阅here

使用jest.advanceTimersByTime()时，如果有大量宏任务通过setTimeout()或setInterval()排队，如果我们想要提前所有计时器，我们必须自己计算 msToRun 毫秒。这也许是非常麻烦的。请参阅“应通过提前所有计时器”测试用例。

此外，有时您可能想在计时器执行之前检查状态。在这种情况下，您必须使用 jest.advanceTimersByTime()，请参阅此 real world example ，定时器是200毫秒，但他们在199毫秒内检查快进的状态。

jest.advanceTimersToNextTimer() 使用 click.next() @sinonjs/faker-timers 包底层的方法。

Advances the clock to the the moment of the first scheduled timer, firing it.

jest.advanceTimersByTime()只需使用 clock.tick(time)底层。

请参阅下面的示例，三个测试用例以不同的方式执行相同的操作。

describe('71667406', () => {
  beforeAll(() => {
    jest.useFakeTimers();
  });
  afterAll(() => {
    jest.useRealTimers();
  });
  describe('advanceTimersToNextTimer', () => {
    test('should pass', () => {
      const runOrder: Array<string> = [];
      const mock1 = jest.fn(() => runOrder.push('mock1'));
      const mock2 = jest.fn(() => runOrder.push('mock2'));
      const mock3 = jest.fn(() => runOrder.push('mock3'));
      const mock4 = jest.fn(() => runOrder.push('mock4'));

      setTimeout(mock1, 100);
      setTimeout(mock2, 0);
      setTimeout(mock3, 0);
      setInterval(() => {
        mock4();
      }, 200);

      jest.advanceTimersToNextTimer();
      // Move forward to t=0
      expect(runOrder).toEqual(['mock2', 'mock3']);

      jest.advanceTimersToNextTimer();
      // Move forward to t=100
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1']);

      jest.advanceTimersToNextTimer();
      // Move forward to t=200
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1', 'mock4']);

      jest.advanceTimersToNextTimer();
      // Move forward to t=400
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1', 'mock4', 'mock4']);
    });

    test('should pass with steps', () => {
      const runOrder: Array<string> = [];
      const mock1 = jest.fn(() => runOrder.push('mock1'));
      const mock2 = jest.fn(() => runOrder.push('mock2'));
      const mock3 = jest.fn(() => runOrder.push('mock3'));
      const mock4 = jest.fn(() => runOrder.push('mock4'));

      setTimeout(mock1, 100);
      setTimeout(mock2, 0);
      setTimeout(mock3, 0);
      setInterval(() => {
        mock4();
      }, 200);

      jest.advanceTimersToNextTimer(4);
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1', 'mock4', 'mock4']);
    });
  });

  describe('advanceTimersByTime', () => {
    test('should pass', () => {
      const runOrder: Array<string> = [];
      const mock1 = jest.fn(() => runOrder.push('mock1'));
      const mock2 = jest.fn(() => runOrder.push('mock2'));
      const mock3 = jest.fn(() => runOrder.push('mock3'));
      const mock4 = jest.fn(() => runOrder.push('mock4'));

      setTimeout(mock1, 100);
      setTimeout(mock2, 0);
      setTimeout(mock3, 0);
      setInterval(() => {
        mock4();
      }, 200);

      jest.advanceTimersByTime(0);
      // Move forward to t=0
      expect(runOrder).toEqual(['mock2', 'mock3']);

      jest.advanceTimersByTime(100);
      // Move forward to t=100
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1']);

      jest.advanceTimersByTime(200);
      // Move forward to t=200
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1', 'mock4']);

      jest.advanceTimersByTime(200);
      // Move forward to t=400
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1', 'mock4', 'mock4']);
    });

    test('should pass advance all timers', () => {
      const runOrder: Array<string> = [];
      const mock1 = jest.fn(() => runOrder.push('mock1'));
      const mock2 = jest.fn(() => runOrder.push('mock2'));
      const mock3 = jest.fn(() => runOrder.push('mock3'));
      const mock4 = jest.fn(() => runOrder.push('mock4'));

      setTimeout(mock1, 100);
      setTimeout(mock2, 0);
      setTimeout(mock3, 0);
      setInterval(() => {
        mock4();
      }, 200);

      // We need to calculate it, this is very cumbersome
      jest.advanceTimersByTime(0 + 100 + 200 + 200);
      expect(runOrder).toEqual(['mock2', 'mock3', 'mock1', 'mock4', 'mock4']);
    });
  });
});

测试结果:

 PASS  stackoverflow/71667406/index.test.ts
  71667406
    advanceTimersToNextTimer
      ✓ should pass (4 ms)
      ✓ should pass with steps
    advanceTimersByTime
      ✓ should pass (1 ms)

Test Suites: 1 passed, 1 total
Tests:       3 passed, 3 total
Snapshots:   0 total
Time:        1.242 s

也希望Jest官方能够给出更多的例子来说明API的使用场景。