Jest：尽管期望/接收值不匹配，但异步测试错误地通过

Question

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，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

从 .then() 中删除 async/await。没有不同。

Answer 1

测试在Promise回调运行之前完成，所以它通过了......然后错误被记录下来。

如果测试包含异步代码，则您需要使用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');
    })
});

...或者使用async测试功能和await在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');
});