javascript - Promise resolve 后如何正确测试 setTimeout

Question

如何正确测试此功能。

1. 设置超时
2. 超时回调
3. 和递归调用

export function initScheduler(timeout: number, callback: () => Promise<void>): void {
  setTimeout(() => {
    callback().then(() => {
      initScheduler(timeout, callback);
    });
  }, timeout);
}

我试过类似的东西

describe('initScheduler', () => {
  it('should call on schedule', () => {
    jest.useFakeTimers();

    const timeout: number = 60000;
    const callback: jest.Mock = jest.fn().mockResolvedValue(undefined);

    initScheduler(timeout, callback);

    expect(setTimeout).toHaveBeenCalledTimes(1);
    expect(setTimeout).toHaveBeenLastCalledWith(expect.any(Function), timeout);
    expect(callback).not.toBeCalled();

    jest.advanceTimersByTime(timeout);

    expect(callback).toBeCalled();
    expect(setTimeout).toHaveBeenCalledTimes(2);
  });
});

但最后的期望返回 1

Answer 1

不要专注于针对 setTimeout 的断言.专注于您的职能应该做什么。

describe('', () => {
  jest.useFakeTimers();
  const timeout = 300;
  const callback = jest.fn();

  beforeEach(() => {
    jest.clearAllTimers();
    callback
      .mockClear()
      .mockReturnValue(Promise.resolve()); 
  });

  it('runs callback only after delay given', () => {
    initScheduler(timeout, callback);
    jest.advanceTimersByTime(timeout - 1);
    expect(callback).not.toHaveBeenCalled();
    jest.advanceTimersByTime(2);
    expect(callback).toHaveBeenCalledTimes(1);
  });

  it('reruns scheduler if callback been resolved successfully', async () => {
    initScheduler(timeout, callback);
    expect(callback).not.toHaveBeenCalled();
    jest.advanceTimersByTime(timeout);
    await Promise.resolve();
    jest.advanceTimersByTime(timeout);
    await Promise.resolve();
    jest.advanceTimersByTime(timeout);
    await Promise.resolve();
    expect(callback).toHaveBeenCalledTimes(3);
  });

  it('stops scheduler if callback rejected', async () => {
    callback.mockReturnValue(Promise.reject());
    initScheduler(timeout, callback);
    jest.advanceTimersByTime(timeout);
    await Promise.resolve();
    jest.advanceTimersByTime(timeout);
    await Promise.resolve();
    expect(callback).toHaveBeenCalledTimes(1);
  });
});

一些细节。

1. 我很惊讶，但计时器在 it() 之间没有被清除。对我来说没有jest.clearAllTimers() .可能取决于 jsdom实现或 jest版本，我不知道。
2. 没有await Promise.resolve()你的模拟 callback不要运行 .then部分。实际上它可能是await <anything else> , 我只看到 await Promise.resolve();看起来不如 await 42; 神奇.不管怎样，它的目的是冲洗microtasks queue虽然开 Jest 本身 does not provide直接的API。