JestJS - Trying to Mock Async Await in Node JS Tests

Question

I am attempting to use Jest for my Node Js Test (specifically AWS's Lambda) but I am having difficulty mocking async await functionality.

I am using babel-jest and jest-cli. Below are my modules. I am getting to the first console.log, but the second console.log returns undefined and my test crash.

Any ideas on how to implement this?

Below is my module:

import {callAnotherFunction} from '../../../utils';

  export const handler = async (event, context, callback) => {

  const {emailAddress, emailType} = event.body;
  console.log("**** GETTING HERE = 1")
  const sub = await callAnotherFunction(emailAddress, emailType);
  console.log("**** Not GETTING HERE = 2", sub) // **returns undefined**

  // do something else here
  callback(null, {success: true, returnValue: sub})

}

My Test

import testData from '../data.js';
import { handler } from '../src/index.js';
jest.mock('../../../utils');

beforeAll(() => {
  const callAnotherLambdaFunction= jest.fn().mockReturnValue(Promise.resolve({success: true}));
});

describe('>>> SEND EMAIL LAMBDA', () => {
  test('returns a good value', done => {
    function callback(dataTest123) {
      expect(dataTest123).toBe({success: true, returnValue: sub);
      done();
    }

    handler(testData, null, callback);
  },10000);
})

Answer 1

You should be careful about somethings below:

• Import your utils as a module then mock callAnotherLambdaFunction function

• Mock return value of callAnotherLambdaFunction with Resolve and Reject case https://jestjs.io/docs/en/mock-function-api.html#mockfnmockresolvedvaluevalue

This is my example:

import testData from '../data.js';
import { handler } from '../src/index.js';
import * as Utils from '../../../utils'


jest.mock('../../../utils');
beforeAll(() => {
  Utils.callAnotherLambdaFunction = jest.fn().mockResolvedValue('test');
});

describe('>>> SEND EMAIL LAMBDA', () => {
  it('should return a good value', async () => {
    const callback = jest.fn()
    await handler(testData, null, callback);
    expect(callback).toBeCalledWith(null, {success: true, returnValue: 'test'})
  });
})