test an async function has thrown an exception using sinon and chai

Question

I have this exported function:

module.exports.doThing = async (input) => {
  if(input === '') { throw('no input present') }
  // other stuff
  return input
}

and a test file for it, in which I'm trying to test that an error is thrown when input is invalid. This is what I've tried:

const testService = require('../services/testService.js')
const chai = require('chai')
const expect = chai.expect
const sinon = require('sinon')
chai.use(require('sinon-chai'))

describe('doThing', () => {
  it('throws an exception if input is not present', async () => {
    expect(testService.doThing('')).to.be.rejected
  })
})

I'm getting the error Error: Invalid Chai property: rejected and also UnhandledPromiseRejectionWarning

How can I fix this test?

Answer 1

You can to install the plugin chai-as-promised. This allows you to do the following:

const testService = require('../services/testService.js')
const chai = require('chai')
    .use(require('chai-as-promised'))
const expect = chai.expect;

describe('doThing', () => {
    it('throws an exception if input is not present', async () => {
        await expect(testService.doThing('')).to.be.rejectedWith('no input present');
    });
    it('should not throw ...', async () => {
        await expect(testService.doThing('some input')).to.be.fulfilled;
    });
})