Stubbing MQTT.js library in Ember.js tests with Sinon.JS


I took the opportunity to upgrade the ember-mqttjs support to Ember v4 for refactoring the addons tests. During last EmberFest (which happened in Rome on Sept. 30 and Oct. 1, 2021) I listened to a lot of brilliant talks. One of them caught my attention because it dealt with the testing topic and in particular of mocks and stubs.

Gonçalo Morais dove into this argument with some stunning hints during his talk “Mock & Roll” that opened my minds and let me wondering on how to improve my mqtt ember addon tests.

After some experiments with the mock-socket library I realized that this tool was not anymore mantained and combining some searchs into the Sinon.JS documentation I found a way to stub the MQTT.js dependency faking the connect method.

This method returns a client and triggers some events that are useful to understand the mqtt connection status. Joining the replace and fake methods from Sinon.JS I found a way to simulate the MQTT.js connect method behavior returning a client with the necessary methods and triggering the needed events.

As you can see next on the code sample attached to this post I need to add some tricks to the joke, because for example the connect event needs to be trigger after a delay while the fake client declares an event handler that must to be there when the event is fired. Or for example the subscribe and publish methods need to call a callback with the correct parameters.

Once I discovered this tricks the tests runs correctly and I can assume that my code is working fine relying on the MQTT.js client to be properly tested.

Code sample

This is the example for the connect test but you can find the whole code into the addon repository:

import { module, test } from 'qunit';
import { setupTest } from 'ember-qunit';
import sinon from 'sinon';
import mqttjs from 'mqtt/dist/mqtt';
import Service from '@ember/service';
import Evented from '@ember/object/evented';
import { later } from '@ember/runloop';

class MqttServiceStub extends Service.extend(Evented) {}

module('Unit | Service | mqtt', function (hooks) {
  let mqttHost = 'ws://localhost:8883';
  let mqttTopic = 'presence';
  let mqttMessage = 'Hello';

  let mqttServiceStub;


  hooks.afterEach(() => {

  // ...

  //Testing mqtt connect
  test('mqtt connect success', async function (assert) {
    let service = this.owner.lookup('service:mqtt');
    let done = assert.async();
    mqttServiceStub = new MqttServiceStub();
      sinon.fake(() => {
        later(() => {
        }, 100);
        return {
          on: (sEvent) => {
            mqttServiceStub.on(sEvent, () => {
              if (sEvent === 'connect') {
                return service.onConnect();
    try {
      service.on('mqtt-connected', () => {
      await service.connect(mqttHost);
    } catch {
    } finally {

If you notice some errors or you need more informations about the code I’m happy to hear from you. Reach me through my contact page.

Ember + Boostrap 5

Today I welcome a new template for my blog by returning to write a post after a very long time!

This WordPress theme is built on top of the latest Bootstrap release, Bootstrap 5 and with this post I would like to explain you how to use this hugely popular front-end framework in an Ember app.

With this major new release the developers have focused most of their efforts towards removing jQuery as a dependency of the framework to make it lighter and usable by a wider audience now interested in saving as much kb as possible.

For those who knows and uses the previous Bootstrap version (v4) I suggest to dive into the migration guide, to understand what breaking changes were made in this new update.

As an experiment (I will tell you later about what I am working on in my spare time) I’ve tried to use Bootstrap 5 in a new Ember Octane app and thank to the release of the bootstrap npm package this turned out to be tremendously simple.

Let’s see the steps:

First you have to install the bootstrap npm package:

npm install --save-dev bootstrap

Then you have to modify your ember-cli-build.js file:

'use strict';

const EmberApp = require('ember-cli/lib/broccoli/ember-app');

module.exports = function (defaults) {
  let app = new EmberApp(defaults, {
    // Add options here
    sassOptions: {
      includePaths: ['node_modules/bootstrap/scss'],
  return app.toTree();

The last few steps are required to be able to import bootstrap SCSS files.
First you have to install ember-cli-sass addon:

ember install ember-cli-sass

Then you have to rename your app style app.css to app.scss and insert the line to import the bootstrap files:

@import 'bootstrap';

You are now ready to use Bootstrap 5 in your Ember app!