javascript - Jest 单元测试 - 如何在 setTimeout 重复函数中调用异步函数

Question

更新:可以肯定地说这基本上是 Jest: Timer and Promise don't work well. (setTimeout and async function) 的副本

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我有一个函数在执行异步函数后会自行重复。我想验证 jest.advanceTimersOnTime(5000) 继续产生 expect(doAsyncStuff).toHaveBeenCalledTimes(X);。

我观察到我们可以调用 repeat 函数，但在请求 jest 提前计时器时它不会“通过”。当您删除它前面的异步函数时，它确实有效。所以听起来我必须让 doAsyncStuff 在这里“调用”或解决一些悬而未决的 promise ？

函数

function repeatMe() {
    setTimeout(() => {
        doAsyncStuff.then((response) => {
            if (response) {
                console.log("I get here!");
                repeatMe();
            }
        })
    }, 5000);
}

测试

jest.useFakeTimers();

let doAsyncStuff = jest.spyOn(updater, 'doAsyncStuff');
doAsyncStuff.mockResolvedValue(true);

repeatMe();

jest.advanceTimersByTime(5000);
expect(doAsyncStuff).toHaveBeenCalledTimes(1);

jest.advanceTimersByTime(5000);
expect(doAsyncStuff).toHaveBeenCalledTimes(2); // Failed?

Answer 1

So it sounds like I have to...resolve some pending promise here?

是的，完全正确。

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简短的回答是 Promise 回调在 PromiseJobs 中排队。通过链接到 doAsyncStuff 返回的 Promise 的 then，以及编写测试的方式，那个回调永远没有机会运行直到测试已经结束。

要修复它，请在测试期间给 Promise 回调一个运行的机会:

更新器.js

export const doAsyncStuff = async () => { };

代码.js

import { doAsyncStuff } from './updater';

export function repeatMe() {
  setTimeout(() => {
    doAsyncStuff().then((response) => {
      if (response) {
        console.log("I get here!");
        repeatMe();
      }
    })
  }, 5000);
}

代码.test.js

import * as updater from './updater';
import { repeatMe } from './code';

test('repeatMe', async () => {
  jest.useFakeTimers();

  let doAsyncStuff = jest.spyOn(updater, 'doAsyncStuff');
  doAsyncStuff.mockResolvedValue(true);

  repeatMe();

  jest.advanceTimersByTime(5000);
  expect(doAsyncStuff).toHaveBeenCalledTimes(1);  // Success!

  await Promise.resolve();  // let callbacks in PromiseJobs run

  jest.advanceTimersByTime(5000);
  expect(doAsyncStuff).toHaveBeenCalledTimes(2);  // Success!

  await Promise.resolve();  // let callbacks in PromiseJobs run

  jest.advanceTimersByTime(5000);
  expect(doAsyncStuff).toHaveBeenCalledTimes(3);  // Success!

  // ... and so on ...
});

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可以在 my answer here 中找到关于究竟发生了什么以及为什么会发生的完整细节。