当我尝试测试我的重试 util 函数时，jest.advanceTimersByTime 不起作用

Question

我有一个想要测试的重试实用程序功能。看起来是这样的

export const sleep = (t: number) => new Promise((r) => setTimeout(r, t));

type RetryFn = (
  fn: Function,
  config: {
    retryIntervel: number;
    retryTimeout: number;
    predicate: Function;
    onRetrySuccess?: Function;
    onRetryFail?: Function;
  }
) => Promise<any>;

export const retry: RetryFn = async (
  fn,
  { predicate, onRetrySuccess, onRetryFail, retryIntervel, retryTimeout }
) => {
  const startTime = Date.now();
  let retryCount = 0;
  while (Date.now() - startTime < retryTimeout) {
    try {
      const ret = await fn();
      if (predicate(ret)) {
        if (retryCount > 0) onRetrySuccess && onRetrySuccess();
        return ret;
      } else {
        throw new Error();
      }
    } catch {
      retryCount++;
    }
    await sleep(retryIntervel);
  }
  if (onRetryFail) onRetryFail();
};

它的作用是在给定的时间间隔内重试该函数。

我想我可以使用jest.advanceTimersByTime 来提前计时器以测试重试发生了多少次。

import { retry } from "./index";

const value = Symbol("test");

function mockFnFactory(numFailure: number, fn: Function) {
  let numCalls = 0;
  return function () {
    fn();
    numCalls++;
    if (numCalls <= numFailure) {
      console.log("numCalls <= numFailure");

      return Promise.resolve({ payload: null });
    } else {
      console.log("numCalls => numFailure");

      return Promise.resolve({
        payload: value
      });
    }
  };
}

describe("retry function", () => {
  beforeEach(() => {
    jest.useFakeTimers();
  });
  it("retrys function on 1st attempt, and succeed thereafter", async () => {
    const fn = jest.fn();
    const onRetrySuccessFn = jest.fn();
    const mockFn = mockFnFactory(3, fn);
    retry(mockFn, {
      predicate: (res: any) => res.payload === value,
      onRetrySuccess: onRetrySuccessFn,
      retryIntervel: 1000,
      retryTimeout: 5 * 60 * 1000
    });
    jest.advanceTimersByTime(1000);
    expect(fn).toHaveBeenCalledTimes(1);
    expect(onRetrySuccessFn).not.toHaveBeenCalled();
    jest.advanceTimersByTime(1000);
    expect(fn).toHaveBeenCalledTimes(2); // ???? fail
    expect(onRetrySuccessFn).not.toHaveBeenCalled();
    jest.advanceTimersByTime(2000);
    expect(fn).toHaveBeenCalledTimes(3);// ???? fail
    expect(onRetrySuccessFn).toHaveBeenCalledTimes(1);
  });
});

但似乎无论我将计时器提前多少，该函数都只会被调用一次。

您可以在https://codesandbox.io/s/lucid-knuth-e810e?file=/src/index.test.tshttps://codesandbox.io/s/lucid-knuth-e810e?file=/src/index.test.tscodesandbox 上找到代码

但是，有一个已知的 issue 带有代码框，它不断抛出此错误 TypeError: jest.advanceTimersByTime is not a function 。此错误不会在本地出现。

Answer 1

因为this。

这是我在测试帮助文件中使用的内容：

const tick = () => new Promise(res => setImmediate(res));

export const advanceTimersByTime = async time => jest.advanceTimersByTime(time) && (await tick());

export const runOnlyPendingTimers = async () => jest.runOnlyPendingTimers() && (await tick());
 
export const runAllTimers = async () => jest.runAllTimers() && (await tick());

在我的测试文件中，我导入了我的助手，而不是调用jest.advanceTimersByTime，而是我的awaitadvanceTimersByTime 函数。

在你的具体例子中，你只需要在调用advanceTimersByTime 之后给await 一个函数——就像这样：

// top of your test file
const tick = () => new Promise(res => setImmediate(res));

... the rest of your existing test file

    jest.advanceTimersByTime(1000);
    expect(fn).toHaveBeenCalledTimes(1);
    expect(onRetrySuccessFn).not.toHaveBeenCalled();
    jest.advanceTimersByTime(1000);
    await tick(); // this line
    expect(fn).toHaveBeenCalledTimes(2);
    expect(onRetrySuccessFn).not.toHaveBeenCalled();
    jest.advanceTimersByTime(2000);
    await tick(); // this line
    expect(fn).toHaveBeenCalledTimes(3)
    expect(onRetrySuccessFn).toHaveBeenCalledTimes(1);