如何使用 sinon 测试异步方法

Question

I'm unit testing a function which is calling another async task inside it without await. The reason for that is because I don't want to wait for that function execution.

const fn1 = async () => {
  fn2();
  return 'foo';
};

const fn2 = async () => {
  await fn3();
  await fn4();
};

const fn3 = async () => {
  await s3.upload(params).promise();
};

const fn4 = async () => {
  await s3.upload(params).promise();
};

I want to unit test fn1() & fn2() is an async task, & here is what I've tried:

describe("unit test fn1", () => {
  
  let s3Stub;
   
  beforeEach(() => {
     s3Stub = sinon.stub(S3, "upload");
 });

  afterEach(() => {
    s3Stub.restore();
 });
  
  it("fn1 test" , async () => {
     const actualValue = await fn1();
     expect(s3Stub.calledTwice).to.be.true; 
  });

});

Ideally, the s3Stub should have been called twice, but is being called only once & my test gets completed.

I don't want to use await on fn2(), as I want fn2() to be run as an independent thread. Any ideas on how do we unit test on such cases?

Answer 1

unit test solution for testing fn1 and fn2 :

index.js :

const s3 = require('./s3');

const fn1 = async () => {
  exports.fn2();
  return 'foo';
};

const fn2 = async () => {
  await exports.fn3();
  await exports.fn4();
};

const fn3 = async () => {
  await s3.upload(params).promise();
};

const fn4 = async () => {
  await s3.upload(params).promise();
};

exports.fn1 = fn1;
exports.fn2 = fn2;
exports.fn3 = fn3;
exports.fn4 = fn4;

s3.js :

const s3 = {
  upload() {
    return this;
  },
  async promise() {},
};

module.exports = s3;

index.test.js :

const fns = require('./');
const sinon = require('sinon');
const { expect } = require('chai');

describe('64705245', () => {
  afterEach(() => {
    sinon.restore();
  });
  describe('fn1', () => {
    it('should return foo', async () => {
      const fn2Stub = sinon.stub(fns, 'fn2').resolves();
      const actual = await fns.fn1();
      expect(actual).to.be.equal('foo');
      sinon.assert.calledOnce(fn2Stub);
    });
  });

  describe('fn2', () => {
    it('should pass', async () => {
      const fn3Stub = sinon.stub(fns, 'fn3').resolves();
      const fn4Stub = sinon.stub(fns, 'fn4').resolves();
      await fns.fn2();
      sinon.assert.calledOnce(fn3Stub);
      sinon.assert.calledOnce(fn4Stub);
    });
  });
});

unit test result:

  64705245
    fn1
      ✓ should return foo
    fn2
      ✓ should pass


  2 passing (16ms)

----------|---------|----------|---------|---------|-------------------
File      | % Stmts | % Branch | % Funcs | % Lines | Uncovered Line #s 
----------|---------|----------|---------|---------|-------------------
All files |   83.33 |      100 |   33.33 |   83.33 |                   
 index.js |   86.67 |      100 |      50 |   86.67 | 14,18             
 s3.js    |   66.67 |      100 |       0 |   66.67 | 3                 
----------|---------|----------|---------|---------|-------------------