javascript - 测试使用 setTimeout 和 Jest : why is this test failing? 的函数

Question

我有一个 rateLimit 函数(它只是 this code 的修改版本):

function rateLimit(func, wait) {
    var timeout;
    return function () {
        var context = this;
        var args = arguments;
        var later = function () {
            timeout = null;
            func.apply(context, args);
        };
        clearTimeout(timeout);
        timeout = setTimeout(later, wait);
    };
}

此功能在我的应用程序中运行良好，所以我相当确定实现是好的。但是，以下测试失败:

jest.useFakeTimers();

test('rateLimit', () => {
    const action = jest.fn();

    const doAction = rateLimit(action, 100);

    doAction(); // This should increment the call count
    doAction(); // This shouldn't, because 100ms hasn't elapsed yet

    jest.advanceTimersByTime(101);

    doAction(); // This should increment the count again

    expect(action).toHaveBeenCalledTimes(2);
});

出现错误:

Expected mock function to have been called two times, but it was called one time.

Here is a runnable version of this code on repl.it .

我在这里做错了什么？

Answer 1

您的速率限制器使用 trailing 方法，当新调用进入时，它会取消当前正在进行的任何调用...直到等待时间到期，此时函数被调用。

您只需要再次提前计时器以便再次调用该函数:

jest.useFakeTimers();

test('rateLimit', () => {
    const action = jest.fn();

    const doAction = rateLimit(action, 100);

    doAction(); // This should increment the call count
    doAction(); // This shouldn't, because 100ms hasn't elapsed yet

    jest.advanceTimersByTime(101);

    doAction(); // This should increment the count again

    jest.advanceTimersByTime(101);  // <= advance the timers again

    expect(action).toHaveBeenCalledTimes(2);  // Success!
});