开玩笑：尽管期望/接收值不匹配，但异步测试错误地通过答案

【问题标题】：Jest: async test incorrectly passes despite mismatched expect/received values开玩笑：尽管期望/接收值不匹配，但异步测试错误地通过
【发布时间】：2019-06-09 07:14:39
【问题描述】：

Jest 中的以下测试不应通过：

const targetFile = require("../targetFile.js");
fetch = jest.fn(() => Promise.resolve('file scoped default value'));

test('diffFileFetch', () => {
  fetch.mockImplementation(() => new Promise((resolve, reject) => {
    resolve('wrong value');
  }));

  targetFile.diffFileFetch()
    .then(async data => {
      await expect(data).toEqual('correct value');
    })
    .catch(e => console.log(e, `=====e=====`));
});

catch 块触发，但测试仍然通过。这是什么原因造成的，应该如何解决？

PASS  
views/admin/__tests__/CurrentCouponListingSection.test.js
  ✓ diffFileFetch (6ms)

 console.log views/admin/__tests__/testFile.test.js:59
    { Error: expect(received).toEqual(expected) // deep equality

    Expected: "correct value"
    Received: "wrong value"
        at targetFile.diffFileFetch.then (/var/www/html/wptest2/wp-content/plugins/fvc/views/admin/__tests__/testFile.test.js:58:1)
        at <anonymous>
        at process._tickCallback (internal/process/next_tick.js:188:7)
      matcherResult: 
       { actual: 'wrong value',
         expected: 'correct value',
         message: [Function],
         name: 'toEqual',
         pass: false } } '=====e====='

也试过了

从 .then() 中移除 async/await。没有区别。

【问题讨论】：

标签： javascript jestjs

【解决方案1】：

测试在 Promise 回调运行之前完成，因此它通过了...然后记录错误。

如果测试包含异步代码，那么您需要使用done：

test('diffFileFetch', done => {  // <= use done
  fetch.mockImplementation(() => new Promise((resolve, reject) => {
    resolve('wrong value');
  }));

  targetFile.diffFileFetch()
    .then(data => {
      expect(data).toBe('correct value');
      done();  // <= now call done
    })
});

...返回Promise:

test('diffFileFetch', () => {
  fetch.mockImplementation(() => new Promise((resolve, reject) => {
    resolve('wrong value');
  }));

  return targetFile.diffFileFetch()  // <= return the Promise
    .then(data => {
      expect(data).toBe('correct value');
    })
});

...或使用async 测试函数和await Promise：

test('diffFileFetch', async () => {  // <= async test function
  fetch.mockImplementation(() => new Promise((resolve, reject) => {
    resolve('wrong value');
  }));

  const data = await targetFile.diffFileFetch()  // <= await the Promise
  expect(data).toBe('correct value');
});

【讨论】：