Top 10 React Testing Tools and Libraries in 2019

Top 10 React Testing Tools and Libraries in 2019

In this article, you'll see useful frameworks, libraries and tools for testing your React components and application in 2019

In this article, you'll see useful frameworks, libraries and tools for testing your React components and application in 2019

Most people use Jest to test their components. Probably, with Enzyme and a couple of other utils. But, while FB recommends Jest as their React testing Framework of choice, the open source ecosystem for testing React applications is rich in frameworks and tools.

From various JavaScript testing frameworks to useful assertion libraries, choosing the right toolset is key in leveraging TDD in React, from component unit-testing to integration testing and even end-to-end testing React apps.

To help navigate the landscape, here are some popular Testing frameworks and libraries for React. Please feel free to comment and suggest your own favorite tools, or share your insights from working with any of them.

1. Jest

Jest is the testing framework used at Facebook to test React components and is adopted by Uber, Airbnb and other teams. The React community, therefore, recommends Jest as the React testing framework of choice. Jest itself works with many JavaScript projects our of the box, from create-react-app to NG, Vue and even TS or Babel.

Jest’s UI snapshot testing and complete-API philosophy combines well with React. Performance is also a plus with process-based parallel testing and optional priority to failed tests. With over 16M downloads a week, Jest is probably the most popular testing framework for React.

2. Mocha

Mocha is a JavaScript test framework for Node.js programs, featuring browser support, asynchronous testing, test coverage reports, and use of any assertion library. It is very configurable and gives the developer full control over how they wish to test their code, with which tools, while you can plug in and out most supporting libraries and tools in your chain.

Just like Jest and other frameworks, when used it React, Mocha can be combined with Enzyme, and also with Chai and other libraries for assertion, mocking etc. Some prefer it to test their React apps as well, often when in need of specific advanced configurations with a mature and rich toolset. Yet, this also can become a pain, as common tasks (like snapshots) will require adding more tools and further configurations in your workflow.

Github

3. Chai

Chai is a BDD / TDD assertion and expectation library for node and the browser that can be delightfully paired with any javascript testing framework. It’s often associated with testing in Mocha with Enzyme, and can also be used with Jest and Enzyme. Chai’s basic interfaces include functionalities such as expect, should and assert, helping you to declare what to expect in a test. If choosing Mocha as your testing framework, it can be useful to give it a try.

Github

4. Karma

Karma is not a testing framework or an assertion library (works with Jasmine, Mocha etc). It launches an HTTP server, and generates the test runner HTML file. With Karma, you can execute JavaScript code in multiple real browsers.

It was built to simplify the feedback loop between writing code and getting information from your tests, without having to dabble in configurations. You can run tests locally and check them in real browsers and devices, from your phone to tablets and desktops, while the entire feedback loop happens in your IDE. Karma also works with continuous integration to Jenkins, Travis etc.

Github

5. Jasmine

Jasmine defines itself as a “JavaScript testing framework for browsers and node.js”.It’s a Behavior Driven Development testing framework for JavaScript. It does not rely on browsers, DOM, or any JavaScript framework. However, it’s been traditionally used in Frameworks like Angular with their CLI tool.

Jasmine can be used to test React applications, for example with Babel and Enzyme. There’s even a designated helper util library built to make this workflow smoother. Asking yourself whether or not there’s a reason to choose Jasmine over Jest?

Github

6. Enzyme

It’s hard to dive into React testing, and particularly with testing frameworks like Jest, without crossing paths with Enzyme by AirbnbEng. Enzyme isn’t a testing framework, but rather a testing utility for React that makes it easier to test the outputs of components, abstracting the rendering of components.

Much like JQuery used to do on the DOM, Enzyme lets you manipulate, traverse, and in some ways simulate runtime given the output. In short, it can really help you render components, find elements and interact with them.

Github

7. React-testing-library

For those of you who don’t use Enzyme, like Facebook itself, the React team recommends using the react-testing-library to simulate user behavior in your tests. Much like Enzyme, this library is a simple and complete set of React DOM testing utilities aimed to imitate actual user actions and workflows. Choosing between react-testing-library an Enzyme?

Github

8. React test utils and test renderer

True, this isn’t a library but rather a collection of useful utilities (like act(), mockComponent(), isElement and more) in React that help to test components using a testing framework of your choice. Test renderer lets you render React components into pure JavaScript objects without depending on the DOM.

Knowledge of these useful tools is key in successfully testing your components and apps in React, and without having to force external tools into doing more than they should. Your decision-tree journey should probably start here.

Test Utilities

Test Renderer

9. Cypress IO

Cypress is a JavaScript end-to-end testing framework that makes it easy to setup, write, run and debug tests in the browser. It comes with its own dashboard that gives control over the status of our tests, and, because Cypress works in the actual browser, you can use the browser’s dev tools side-by-side.

You can time-travel with snapshots, automatically reload test changes and await assertions, and easily debug your code. With built-in parallelization and load balancing, Debugging tests in CI becomes much that easier too. However, you can’t use Cypress to drive two browsers at the same time, which might hurt. While not as popular as Puppeteer, Cypress can be useful for end-to-end testing your React applications. This library was even built to make it easier.

Github

10. Pupeeter

Puppeteer is a Node library which provides an API to control Chrome over the DevTools Protocol. Puppeteer runs headless by default but can be configured to run full (non-headless) Chrome or Chromium.

This means, you can use Puppeteer to do pretty much anything you can manually do in the browser, such as generating screenshots, generating pre-rendered content from SPAs and even automating actions like form submissions, keyboard inputs etc.

Puppeteer is often used with Jest (and Faker) to test React applications end-to-end, while puppeteer provides screenshots and more for testing your app.

Github

Conclusion

With the modularity of React comes better TDD. From components to integration and end-to-end testing, choosing the right tooling can help to put this theory into practice without pain, and enjoy its benefits.

Combining the right testing framework (e.g. Jest etc) with the right assertion/manipulation libraries (e.g. Enzyme etc) is the key to creating a smooth yet flexible workflow that can adapt while you upgrade, extend and modify your code. By isolating virtually isolating components from their projects you take modularity and TDD to a whole new level.

JavaScript developers should you be using Web Workers?

JavaScript developers should you be using Web Workers?

Do you think JavaScript developers should be making more use of Web Workers to shift execution off of the main thread?

Originally published by David Gilbertson at https://medium.com

So, Web Workers. Those wonderful little critters that allow us to execute JavaScript off the main thread.

Also known as “no, you’re thinking of Service Workers”.

Photo by Caleb Jones on Unsplash

Before I get into the meat of the article, please sit for a lesson in how computers work:

Understood? Good.

For the red/green colourblind, let me explain. While a CPU is doing one thing, it can’t be doing another thing, which means you can’t sort a big array while a user scrolls the screen.

This is bad, if you have a big array and users with fingers.

Enter, Web Workers. These split open the atomic concept of a ‘CPU’ and allow us to think in terms of threads. We can use one thread to handle user-facing work like touch events and rendering the UI, and different threads to carry out all other work.

Check that out, the main thread is green the whole way through, ready to receive and respond to the gentle caress of a user.

You’re excited (I can tell), if we only have UI code on the main thread and all other code can go in a worker, things are going to be amazing (said the way Oprah would say it).

But cool your jets for just a moment, because websites are mostly about the UI — it’s why we have screens. And a lot of a user’s interactions with your site will be tapping on the screen, waiting for a response, reading, tapping, looking, reading, and so on.

So we can’t just say “here’s some JS that takes 20ms to run, chuck it on a thread”, we must think about where that execution time exists in the user’s world of tap, read, look, read, tap…

I like to boil this down to one specific question:

Is the user waiting anyway?

Imagine we have created some sort of git-repository-hosting website that shows all sorts of things about a repository. We have a cool feature called ‘issues’. A user can even click an ‘issues’ tab in our website to see a list of all issues relating to the repository. Groundbreaking!

When our users click this issues tab, the site is going to fetch the issue data, process it in some way — perhaps sort, or format dates, or work out which icon to show — then render the UI.

Inside the user’s computer, that’ll look exactly like this.

Look at that processing stage, locking up the main thread even though it has nothing to do with the UI! That’s terrible, in theory.

But think about what the human is actually doing at this point. They’re waiting for the common trio of network/process/render; just sittin’ around with less to do than the Bolivian Navy.

Because we care about our users, we show a loading indicator to let them know we’ve received their request and are working on it — putting the human in a ‘waiting’ state. Let’s add that to the diagram.

Now that we have a human in the picture, we can mix in a Web Worker and think about the impact it will have on their life:

Hmmm.

First thing to note is that we’re not doing anything in parallel. We need the data from the network before we process it, and we need to process the data before we can render the UI. The elapsed time doesn’t change.

(BTW, the time involved in moving data to a Web Worker and back is negligible: 1ms per 100 KB is a decent rule of thumb.)

So we can move work off the main thread and have a page that is responsive during that time, but to what end? If our user is sitting there looking at a spinner for 600ms, have we enriched their experience by having a responsive screen for the middle third?

No.

I’ve fudged these diagrams a little bit to make them the gorgeous specimens of graphic design that they are, but they’re not really to scale.

When responding to a user request, you’ll find that the network and DOM-manipulating part of any given task take much, much longer than the pure-JS data processing part.

I saw an article recently making the case that updating a Redux store was a good candidate for Web Workers because it’s not UI work (and non-UI work doesn’t belong on the main thread).

Chucking the data processing over to a worker thread sounds sensible, but the idea struck me as a little, umm, academic.

First, let’s split instances of ‘updating a store’ into two categories:

  1. Updating a store in response to a user interaction, then updating the UI in response to the data change
  2. Not that first one

If the first scenario, a user taps a button on the screen — perhaps to change the sort order of a list. The store updates, and this results in a re-rendering of the DOM (since that’s the point of a store).

Let me just delete one thing from the previous diagram:

In my experience, it is rare that the store-updating step goes beyond a few dozen milliseconds, and is generally followed by ten times that in DOM updating, layout, and paint. If I’ve got a site that’s taking longer than this, I’d be asking questions about why I have so much data in the browser and so much DOM, rather than on which thread I should do my processing.

So the question we’re faced with is the same one from above: the user tapped something on the screen, we’re going to work on that request for hopefully less than a second, why would we want to make the screen responsive during that time?

OK what about the second scenario, where a store update isn’t in response to a user interaction? Performing an auto-save, for example — there’s nothing more annoying than an app becoming unresponsive doing something you didn’t ask it to do.

Actually there’s heaps of things more annoying than that. Teens, for example.

Anyhoo, if you’re doing an auto-save and taking 100ms to process data client-side before sending it off to a server, then you should absolutely use a Web Worker.

In fact, any ‘background’ task that the user hasn’t asked for, or isn’t waiting for, is a good candidate for moving to a Web Worker.

The matter of value

Complexity is expensive, and implementing Web Workers ain’t cheap.

If you’re using a bundler — and you are — you’ll have a lot of reading to do, and probably npm packages to install. If you’ve got a create-react-app app, prepare to eject (and put aside two days twice a year to update 30 different packages when the next version of Babel/Redux/React/ESLint comes out).

Also, if you want to share anything fancier than plain data between a worker and the main thread you’ve got some more reading to do (comlink is your friend).

What I’m getting at is this: if the benefit is real, but minimal, then you’ve gotta ask if there’s something else you could spend a day or two on with a greater benefit to your users.

This thinking is true of everything, of course, but I’ve found that Web Workers have a particularly poor benefit-to-effort ratio.

Hey David, why you hate Web Workers so bad?

Good question.

This is a doweling jig:

I own a doweling jig. I love my doweling jig. If I need to drill a hole into the end of a piece of wood and ensure that it’s perfectly perpendicular to the surface, I use my doweling jig.

But I don’t use it to eat breakfast. For that I use a spoon.

Four years ago I was working on some fancy animations. They looked slick on a fast device, but janky on a slow one. So I wrote fireball-js, which executes a rudimentary performance benchmark on the user’s device and returns a score, allowing me to run my animations only on devices that would render them smoothly.

Where’s the best spot to run some CPU intensive code that the user didn’t request? On a different thread, of course. A Web Worker was the correct tool for the job.

Fast forward to 2019 and you’ll find me writing a routing algorithm for a mapping application. This requires parsing a big fat GeoJSON map into a collection of nodes and edges, to be used when a user asks for directions. The processing isn’t in response to a user request and the user isn’t waiting on it. And so, a Web Worker is the correct tool for the job.

It was only when doing this that it dawned on me: in the intervening quartet of years, I have seen exactly zero other instances where Web Workers would have improved the user experience.

Contrast this with a recent resurgence in Web Worker wonderment, and combine that contrast with the fact that I couldn’t think of anything else to write about, then concatenate that combined contrast with my contrarian character and you’ve got yourself a blog post telling you that maybe Web Workers are a teeny-tiny bit overhyped.

Thanks for reading

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Further reading

An Introduction to Web Workers

JavaScript Web Workers: A Beginner’s Guide

Using Web Workers to Real-time Processing

How to use Web Workers in Angular app

Using Web Workers with Angular CLI


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