如何使用 await 使用 mocha 测试异步代码

Question

How do I test async code with mocha? I wanna use multiple await inside mocha

var assert = require('assert');

async function callAsync1() {
  // async stuff
}

async function callAsync2() {
  return true;
}

describe('test', function () {
  it('should resolve', async (done) => {
      await callAsync1();
      let res = await callAsync2();
      assert.equal(res, true);
      done();
      });
});

This produces error below:

  1) test
       should resolve:
     Error: Resolution method is overspecified. Specify a callback *or* return a Promise; not both.
      at Context.it (test.js:8:4)

If I remove done() I get:

  1) test
       should resolve:
     Error: Timeout of 2000ms exceeded. For async tests and hooks, ensure "done()" is called; if returning a Promise, ensure it resolves. (/tmp/test/test.js)

Answer 1

Mocha supports Promises out-of-the-box ; You just have to return the Promise to it() 's callback.

If the Promise resolves then the test passes. In contrast, if the Promise rejects then the test fails. As simple as that.

Now, since async functions always implicitly return a Promise you can just do:

async function getFoo() {
  return 'foo'
}

describe('#getFoo', () => {
  it('resolves with foo', () => {
    return getFoo().then(result => {
      assert.equal(result, 'foo')
    })
  })
})

You don't need done nor async for your it .

However, if you still insist on using async/await :

async function getFoo() {
  return 'foo'
}

describe('#getFoo', () => {
  it('returns foo', async () => {
    const result = await getFoo()
    assert.equal(result, 'foo')
  })
})

In either case, do not declare done as an argument

If you use any of the methods described above you need to remove done completely from your code. Passing done as an argument to it() hints to Mocha that you intent to eventually call it.

Using both Promises and done will result in:

Error: Resolution method is overspecified. Specify a callback or return a Promise; not both

The done method is only used for testing callback-based or event-based code. You shouldn't use it if you're testing Promise-based or async/await functions.