jestjs - 使用 jest.useFakeTimers 时如何断言回调

Question

我试图了解如何正确地对我们拥有的自定义去抖动方法进行单元测试：

// function we want to test
function debounce(func, wait = 100) {
  let timeout;

  return (...args) => {
    clearTimeout(timeout);
    timeout = setTimeout(() => {
      func.apply(this, args);
    }, wait);
  };
}

这是失败的 Jest 单元测试：

describe('DebounceExample', () => {
  beforeAll(jest.useFakeTimers);
  afterAll(jest.useRealTimers);

  it('should debounce', () => {
    // given
    const data = 'Chuck Norris is faster than you think';
    const debounceTime = 5000;
    const callback = jest.fn();
    const debouncedFunction = debounce(callback, debounceTime);

    // when
    debouncedFunction(data);

    // then
    expect(callback).not.toHaveBeenCalled();

    // when
    jest.runAllTimers(); // jest.advanceTimersByTime(debounceTime);

    // then
    expect(callback).toHaveBeenCalled();
  });
});

失败：

Error: expect(jest.fn()).toHaveBeenCalled()

Expected number of calls: >= 1
Received number of calls:    0  Jest

我也在这里尝试过解决方案：https ://stackoverflow.com/a/52638566/704681没有成功

解决方法：到目前为止我能够测试它的唯一方法：

  it('should denounce - workaround', (done) => {
    // given
    const data = 'Chuck Norris is faster than you think';
    const debounceTime = 5000;
    const callback = jest.fn((param) => {
      // then
      expect(param).toEqual(data);
      done();
    });
    const debouncedFunction = debounce(callback, debounceTime);

    // when
    debouncedFunction(data);

    // then
    expect(callback).not.toHaveBeenCalled();

    // when (see 'then' inside callback implementation)
    jest.runAllTimers(); // jest.advanceTimersByTime(debounceTime);
  });