A test helper for Cloud Functions.
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The deployment of Cloud Functions is very slow. Deployment is normally completed in 30 seconds, but it sometimes take more than 10 minutes. It is a waste of time to wait a few minutes just by rewriting one line.

Cloud Functions Emulator is very useful. However, it is hard to create the test data json, and it is not possible to write tests.

Let's emulate functions locally with rescue-fire and do TDD.


  • Firestore
  • Realtime Database
  • Analytics
  • Auth
  • Pub/Sub
  • Strage


rescue-fire can only create functions.Event <DeltaDocumentSnapshot>. But this is enough to simulate Cloud Functions.
Let's write a Cloud Functions test with this event.


The event created by rescue-fire is not complete. We think that it is enough to write tests, but keep in mind that it is different from the actual event.


npm install rescue-fire --only=dev
yarn add --dev rescue-fire


orderable.ts uses rescue-fire to write tests. please refer. https://github.com/starhoshi/orderable.ts/blob/master/orderable/src/__tests__/orderable.test.ts

1. Prepare Google Cloud Account Credentials

Download the service account key json file.


This json file is sensitive, be careful.

Important: This file contains sensitive information, including your service account's private encryption key. Keep it confidential and never store it in a public repository.

2. Install testing library

Please use your favorite testing library.

For example, in the case of Jest:

npm install jest --only=dev
yarn add --dev jest

3. Write a test

Let's create a function to update name when user is created. The code of the function is as follows.

This sample is written in TypeScript.

const changeName = (event: functions.Event<DeltaDocumentSnapshot>) => {
  console.log('old name', event.data.data().name)
  return event.data.ref.update({ name: 'new name' })

The test will be like this.

import 'jest'
import * as admin from 'firebase-admin'
import * as functions from 'firebase-functions'
import * as Rescue from 'rescue-fire'

// Set up to run firebase in local.
beforeAll(() => {
  const serviceAccount = require('./your-firebase-adminsdk.json')
    credential: admin.credential.cert(serviceAccount)

test('update name', async () => {
  // prepare
  const data = {name: 'name'}
  const user = await admin.firestore().collection('user').add(data)
  const event = Rescue.event(user, data)

  // start Cloud Functions
  await changeName(event)

  // expect name changed
  const updatedUser = await admin.firestore().collection('user').doc(user.id).get()
  expect(updatedUser.data()!.name).toBe('new name')

Cloud Functions can be developed with TDD. 🎉 (strictly not TDD 😄)
This is a very small function, but larger functions can also be developed in this way.

Optional Parameters defenitions is here.

4. Finally, create Functions

exports.updateUser = functions.firestore
  .onCreate(event => {
    return changeName(event)

Let's take a coffee break while deploying.