Testing Library: Everybody Uses It, But Nobody Understands It

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Testing is an essential part of software development, but it can be a tricky and time-consuming process. The popular testing-library package is a widely used tool that helps developers write reliable and maintainable frontend tests based on a behavior driven approach, but many users are not fully aware of how it works. In this talk, I, as one of the maintainers of the package, give an in-depth look into testing-library. You will learn how testing-library is designed to encourage good testing practices and how it can help you write more maintainable tests.

This talk has been presented at TestJS Summit 2023, check out the latest edition of this JavaScript Conference.

FAQ

Js-dom and happy-dom are JavaScript implementations of the DOM used by Testing Library to provide a simulated environment for testing, enabling DOM functionalities that are not natively supported in Node.js.

The getByRole query in Testing Library is crucial because it builds on top of the accessibility tree, allowing developers to query elements based on their roles, both explicit and implicit. This method is recommended for creating robust and user-behavior-mimicking tests.

Testing Library automatically cleans up after each test by unmounting the React tree and removing container references from the document body. This process ensures a fresh and clean environment for subsequent tests.

The speaker learned a valuable lesson about the importance of understanding the internal workings of a tool like Testing Library before attempting to contribute, despite the initial setback of having their commit completely reverted.

The speaker's first meaningful contribution to Testing Library involved resolving a build failure issue with the next version of React, specifically React 17, in the Continuous Integration (CI) process.

Testing Library is a set of simple and complete testing utilities that encourage good testing practices. Its API is designed to ensure tests resemble the way software is used, thereby providing more confidence in the tests' effectiveness.

In a Node environment, which lacks a window object, Testing Library uses js-dom or happy-dom to simulate the DOM. This setup enables the use of window functionalities required by components within the testing environment.

Matan Borenkraout
Matan Borenkraout
22 min
11 Dec, 2023

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Video Summary and Transcription
This Talk is about a developer's first open source contribution to the Testing Library, exploring how it works and its importance in testing. It discusses the challenges of testing in a Node environment and the use of getByRole query to find elements. The Talk also highlights the complexities of implicit roles and the need for specific attributes to filter elements. It emphasizes the importance of verifying visibility and accessibility when querying elements and the process of test clean up.

1. Introduction to Testing Library

Short description:

Hello, everybody! Today, I want to share a short story about my first open source contribution to Testing Library. I found an interesting issue related to the build process and React 17, which led me to debug and make a meaningful contribution. It was an exciting journey into open source development.

Hello, everybody, and thank you so much for joining me remotely today to understand how Testing Library works under the hood.

Before I introduce myself, I want to start with a short story. Once upon a time, it was three years ago, I was looking to make my first open source contribution. I decided to go with a tool that I use on a daily basis, so I decided Testing Library.

While browsing through the issues, I found an interesting one. The issue was a problem in our CI process where the build failed for the next version of React. At the time, it was React 17. I decided that this is an interesting topic. I decided I'll look into it. I debugged both React Testing Library and React to try to understand what happened there and why is our build failing.

A few days later, I had a pull request. It was reviewed and merged, and that was my first meaningful contribution to Testing Library. I remember that day quite clearly. It was around 8 pm. I was extremely happy. I decided I'd go to bed. I was still high on the adrenaline. Didn't sleep quite much, but after a good night's sleep, I woke up happy and cheerful for making my first meaningful contribution. I made my coffee. I sat on my desk. I decided I'd open GitHub and see what happened during the night.

The first thing I saw that caused my mood to immediately change was this issue. Version 10.4.4 causing timeout issue with use effect plus just use fake timers. Then I scrolled a bit more. I saw this one also. Type error, cannot read property, version of undefined and this one also. Schedule function is calling normal priority as a function rather than a callback. And that's not an illustration. All of these issues were open at the night while I was sleeping. And yeah, what a dive into Open Source.

2. Understanding How Testing Library Works

Short description:

In this part, I'll share a story about my open source contribution. I'll then introduce myself and explain how testing library works. We'll align on the basics and discuss the importance of confidence in testing. Let's dive in!

All of them relate directly to my change. They even contain code snippets from the code that I read. And this is an illustration of me at that specific moment. But instead of giving something to Stephen Hawking, I gave it to Ken C. Dodds. And wow, I was ashamed. Luckily for me, this happened around the time React Testing Library had only 1.8 million weekly downloads. So it was nice. At the moment, we have 8.7 million weekly downloads. That's quite a lot.

In this talk I'm going to try and give you some context about how testing library works so you won't make the same mistakes that I made in my first contribution. And don't forget about this story. We'll get back to it at the end.

So after this short story, let's make it official. Hello, everybody. My name is Mattan Boronkraut. I'm a senior software engineer at Microsoft. And today I'm here wearing my testing library maintainer hat to explain to you how testing library works under the hood. If you want to follow me, this is the site where I write some posts. Basically, I write for the draw. I had analytics and I saw that I have around five visits a week, so I decided I'll drop the analytics. I don't want this data in my life. And this is my Twitter handle or x-handle.

So before we dive in, let's align on the basics. So what is testing library? Testing library is a set of simple and complete testing utilities that encourage good testing practices. And our API aims to answer this guiding principle, the more your test resembles the way your software is used, the more confidence they can give you. And we can all agree that confidence is what we're aiming for when we're writing our test. We want to be confident before we're pushing to production. And today we'll understand how we're doing exactly that how we're creating the confidence an API that looks simple on the on top of the surface, but under the hood is quite complex. A few more statistics, DOM testing library, which is our core package.

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