How do you unit test a firebase function wrapped with express?

Question

With firebase functions, you can utilize express to achieve nice functionality, like middleware etc. I have used this example to get inspiration of how to write https firebase functions, powered by express.

However, my issue is that the official firebase documentation on how to do unit testing, does not include a https-express example.

So my question is how to unit test the following function (typescript)?:

// omitted init. of functions
import * as express from 'express';

const cors = require('cors')({origin: true});
const app = express();
app.use(cors);

// The function to test
app.get('helloWorld, (req, res) => {
   res.send('hello world');
   return 'success';
});

exports.app = functions.https.onRequest(app);

Answer 1

This works with Jest

import supertest from 'supertest'
import test from 'firebase-functions-test'
import sinon from 'sinon'
import admin from 'firebase-admin'

let undertest, adminInitStub, request
const functionsTest = test()

beforeAll(() => {
  adminInitStub = sinon.stub(admin, 'initializeApp')
  undertest = require('../index')
  // inject with the exports.app methode from the index.js
  request = supertest(undertest.app)
})

afterAll(() => {
  adminInitStub.restore()
  functionsTest.cleanup()
})

it('get app', async () => {
  let actual = await request.get('/')
  let { ok, status, body } = actual
  expect(ok).toBe(true)
  expect(status).toBeGreaterThanOrEqual(200)
  expect(body).toBeDefined()
})

Answer 2

You can use supertest paired with the guide from Firebase. Below is a very basic example of testing your app, however, you can make it more complex/better by integrating mocha.

import * as admin from 'firebase-admin'
import * as testFn from 'firebase-functions-test'
import * as sinon from 'sinon'
import * as request from 'supertest'
const test = testFn()
import * as myFunctions from './get-tested' // relative path to functions code
const adminInitStub = sinon.stub(admin, 'initializeApp')

request(myFunctions.app)
  .get('/helloWorld')
  .expect('hello world')
  .expect(200)
  .end((err, res) => {
    if (err) {
      throw err
    }
  })