计时器模拟

info" class="reference-link">info

Also see documentation.

In the following example we enable fake timers by calling jest.useFakeTimers(). This is replacing the original implementation of setTimeout() and other timer functions. 计时器可以恢复他们默认的行为通过jest.useRealTimers().

timerGame.js

__tests__/timerGame-test.js

jest.useFakeTimers();
jest.spyOn(global, 'setTimeout');
test('waits 1 second before ending the game', () => {
  const timerGame = require('../timerGame');
  timerGame();
  expect(setTimeout).toHaveBeenCalledTimes(1);
  expect(setTimeout).toHaveBeenLastCalledWith(expect.any(Function), 1000);
});

jest.useFakeTimers();
test('calls the callback after 1 second', () => {
  const timerGame = require('../timerGame');
  const callback = jest.fn();
  timerGame(callback);
  // At this point in time, the callback should not have been called yet
  expect(callback).not.toBeCalled();
  // Fast-forward until all timers have been executed
  jest.runAllTimers();
  expect(callback).toBeCalled();
  expect(callback).toHaveBeenCalledTimes(1);

There are also scenarios where you might have a recursive timer – that is a timer that sets a new timer in its own callback. For these, running all the timers would be an endless loop, throwing the following error: “Aborting after running 100000 timers, assuming an infinite loop!”

If that is your case, using jest.runOnlyPendingTimers() will solve the problem:

infiniteTimerGame.js

__tests__/infiniteTimerGame-test.js

jest.useFakeTimers();
jest.spyOn(global, 'setTimeout');
describe('infiniteTimerGame', () => {
  test('schedules a 10-second timer after 1 second', () => {
    const infiniteTimerGame = require('../infiniteTimerGame');
    const callback = jest.fn();
    infiniteTimerGame(callback);
    // At this point in time, there should have been a single call to
    // setTimeout to schedule the end of the game in 1 second.
    expect(setTimeout).toHaveBeenCalledTimes(1);
    expect(setTimeout).toHaveBeenLastCalledWith(expect.any(Function), 1000);
    // Fast forward and exhaust only currently pending timers
    // (but not any new timers that get created during that process)
    jest.runOnlyPendingTimers();
    // At this point, our 1-second timer should have fired its callback
    expect(callback).toBeCalled();
    // And it should have created a new timer to start the game over in
    // 10 seconds
    expect(setTimeout).toHaveBeenCalledTimes(2);
    expect(setTimeout).toHaveBeenLastCalledWith(expect.any(Function), 10000);
  });

note" class="reference-link">note

jest.useFakeTimers({timerLimit: 100});

另一种可选方式是使用 jeste. advancertimersbytime (msToRun)。通过调用msToRun这个 API时，所有计时器都将以毫秒增长。 When this API is called, all timers are advanced by milliseconds. 所有通过setTimeout() 或setInterval() 而处于任务队列中等待中的“宏任务”和一切其他应该在本时间片中被执行的东西都应该被执行。 Additionally, if those macro-tasks schedule new macro-tasks that would be executed within the same time frame, those will be executed until there are no more macro-tasks remaining in the queue that should be run within msToRun milliseconds.

timerGame.js

__tests__/timerGame-test.js

jest.useFakeTimers();
it('calls the callback after 1 second via advanceTimersByTime', () => {
  const timerGame = require('../timerGame');
  const callback = jest.fn();
  timerGame(callback);
  // At this point in time, the callback should not have been called yet
  expect(callback).not.toBeCalled();
  // Fast-forward until all timers have been executed
  jest.advanceTimersByTime(1000);
  // Now our callback should have been called!
  expect(callback).toBeCalled();
  expect(callback).toHaveBeenCalledTimes(1);
});

最后，在某些测试中你可能需要清除所有等待状态下的定时器，为此，可以使用 jest.clearAllTimers()。 For this, we have jest.clearAllTimers().

/**
 * @jest-environment jsdom
 */
const mockPerformanceMark = jest.fn();
window.performance.mark = mockPerformanceMark;
test('allows mocking `performance.mark()`', () => {
  jest.useFakeTimers({doNotFake: ['performance']});
  expect(window.performance.mark).toBe(mockPerformanceMark);