Two Patterns for Unit Testing Vue Apps

Two Patterns for Unit Testing Vue Apps

Two Patterns for Unit Testing Vue Apps

In this post, we will give you information about Two Patterns for Unit Testing Vue Apps. Here we will give you detail about Two Patterns for Unit Testing Vue Apps And how to use it also give you a demo for it if it is necessary.

At onlinecode, we do our best to test every example in all of our tutorials. That way we can be confident that our content is up to date when major releases happen, or when we decide to rewrite a tutorial. That means we need to automatically test all our Vue examples as well. In general, there are two patterns we use for unit testing our code examples:

With Server-Side Rendering in Node.js

When unit testing, you first need to define what you consider a “unit.” There’s some debate as to what is a unit when it comes to writing Vue code: do individual methods count as units? How about computed properties? We at onlinecode tend to err on the side of testing code closer to how the end user will interact with it, so we consider a Vue component a unit.

Vue enjoys excellent support for Node.js and server-side rendering.
Unlike some other frameworks, instantiating a Vue component in Node.js
doesn’t require any outside libraries or special customization.
Just call new Vue() and you get a Vue instance.

const Vue = require('vue');
const { renderToString } = require('vue-server-renderer').createRenderer();

const app = new Vue({
  data: () => ({ count: 0 }),
  methods: {
    increment: function() { ++this.count; }
  template: '
      <div id="clicks">Clicks: {{count}}</div>
      <button v-on:click="increment()">Increment</button>

let res = await renderToString(app);
assert.ok(res.includes('Clicks: 0'));

// 'app' is reactive in Node
app.count = 2;
res = await renderToString(app);
assert.ok(res.includes('Clicks: 2'));

// You can also call methods in Node
res = await renderToString(app);
assert.ok(res.includes('Clicks: 3'));

The benefit of using Node.js for unit tests is minimal setup and overhead.
The only outside libraries you need are a testing framework like Mocha
and vue-server-renderer.
You can also do a surprising amount with Vue in Node.js: you can $emit
events, change data, call methods, trigger lifecycle hooks, etc.

What you can’t do with Node.js is interact with actual DOM elements,
unless you use another outside library. In the above example, you can
call the method that v-on:click triggers, but you can’t actually
trigger a click event.

With Scaffolding in Puppeteer

Testing Vue apps with Puppeteer is another alternative.
The benefit of using Puppeteer is that you
get a fully fledged browser to work with. You can interact with
your component using vanilla JavaScript APIs like click()
and document.querySelector().

The key idea behind how we test Vue with Puppeteer is Puppeteer’s
setContent() function. If you can bundle everything your component needs,
you can put that JavaScript into a minimal HTML page, and put
it in Puppeteer.

const puppeteer = require('puppeteer');

// Since your Vue app is running in a real browser, you would need
// webpack or browserify to build a bundle if you use 'require()'
const createComponent = function() {
  return new Vue({
    data: () => ({ count: 0 }),
    methods: {
      increment: function() { ++this.count; }
    template: '
        <div id="clicks">Clicks: {{count}}</div>
        <button v-on:click="increment()">Increment</button>

const js = createComponent.toString();
const htmlScaffold = '
      <script src=""></script>

      <div id="content"></div>

      <script type="text/javascript">
        const app = (${js})();

// Launch a new browser and make it render the above HTML.
// You can set 'headless: false' to interact with the real browser.
const browser = await puppeteer.launch({ headless: true });
const page = await browser.newPage();
await page.setContent(htmlScaffold);

// Interact with the component via 'evaluate()'
let content = await page.evaluate(() => {
  return document.querySelector('#clicks').innerHTML.trim()
assert.equal(content, 'Clicks: 0');

await page.evaluate(() => document.querySelector('button').click());

content = await page.evaluate(() => {
  return document.querySelector('#clicks').innerHTML.trim()
assert.equal(content, 'Clicks: 1');

// Clean up
await browser.close();

Testing with Puppeteer is great because you’re testing in a real browser,
which means this test is as realistic as you can get without pointing
and clicking yourself. Also, if you disable headless mode, you can
actually watch the test run.

The downside of testing with Puppeteer is that you need to handle
bundling on your own. The above example doesn’t need to bundle because
it doesn’t use require(), but you would need to use Webpack
or Browserify if
your code uses require(). Even if you use ES6 imports,
getting scaffolding right can be tricky.

Conclusion for Two Patterns for Unit Testing Vue Apps

Vue makes it easy to test components in isolation using Node.js or
Puppeteer. Unit testing with Node.js is easier because it requires
less setup, but you can’t test real browser interactions. On the
other hand, testing with Puppeteer requires more scaffolding, but
makes your tests more realistic.

Vue School has some of our favorite Vue video courses. Their Vue.js Master Class walks you through building a real world application, and does a great job of teaching you how to integrate Vue with Firebase.
Check it out!

Vue.js is a progressive JavaScript framework that makes building user interfaces simple and enjoyable. Vue is designed from the ground up to be incrementally adoptable, so you can use the features you need, and mix and match Vue with other libraries or frameworks.

Vue is a relatively new framework, but it has quickly become one of the most popular JavaScript frameworks in the world. It is used by large companies like Alibaba, Baidu, and Xiaomi, as well as by thousands of smaller businesses and startups.

Here are some of the features that make Vue.js so popular:

  • Declarative rendering: Vue uses a declarative rendering model, which means that you can describe the desired output of your application in terms of HTML, CSS, and JavaScript. This makes it easy to reason about your code and to make changes to your application.
  • Reactivity: Vue is a reactive framework, which means that it automatically updates the DOM whenever there is a change to the application’s state. This makes your application feel fast and responsive.
  • Composition: Vue is a component-based framework, which means that you can build your application out of reusable components. This makes your code more maintainable and easier to test.
  • Performance: Vue is a highly performant framework. It has been benchmarked against other popular JavaScript frameworks, and it has consistently outperformed them.

If you are looking for a JavaScript framework that is easy to learn, powerful, and performant, then Vue.js is a great choice.

Here are some of the things you can do with Vue.js:

  • Build single-page applications
  • Create user interfaces for web, mobile, and desktop applications
  • Integrate with other JavaScript frameworks and libraries
  • Build custom components
  • Create reusable code
  • Test your code

If you are interested in learning more about Vue.js, there are a number of resources available online. The official Vue.js website has a comprehensive documentation and a number of tutorials. There are also a number of third-party websites and blogs that offer tutorials, articles, and other resources about Vue.js.

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