---
title: "Testing your code"
url: "https://www.bekk.christmas/post/2017/02/testing-your-code"
authors: ["Kristofer Giltvedt Selbekk"]
published: "2017-12-02"
updated: "2024-11-07T13:05:28Z"
language: "en-US"
type: "article"
tags: ["React"]
---

# Testing your code

Avoiding bugs in your code is important for the end user experience. Choosing the right way to test your code is paramount!

## In short

Unit testing helps prevent regressions when adding new code or refactoring, and Jest is presented as a fast, stable framework with almost no setup. It also introduces snapshot testing, where you compare a React component tree against a saved rendering instead of writing lots of individual assertions.

- **For:** React developers who want to test their code
- **Good to know beforehand:** Basic JavaScript and React knowledge

_AI-generated_

Unit testing your code is important to avoid introducing bugs whenever you are writing new code or refactoring legacy. When you do it right, you can feel comfortable that edge cases are covered and mission-critical components work as they were intended. Although there are many test frameworks to choose from, [`jest`](https://facebook.github.io/jest/) has risen up as a very attractive candidate. Unlike most test frameworks, there is no setup required, and you can get straight to writing your unit tests.

## But didn't Jest suck?

Jest didn't enjoy its current popularity ratings in its first iterations. However, in 2016 it was totally rewritten to provide a top-notch developer experience, focusing on speed, stability and a super well designed CLI. So you can rest assured - it's nothing like the bad things you might have heard anymore. And Christmas is about forgiveness and all that, right?

## Setup? Done.

As mentioned in [yesterday's article](/2017/01), Jest is included with `create-react-app`. If you have an existing application, however, setting up Jest is easy as peas. Run `npm i --save-dev jest` and add the following to your `package.json` file:

```javascript
"scripts": {
    // Run your test suite
    "test": "jest",
    // Start an iterative test watcher
    "test:watch": "jest --watch",
    // Run tests, outputting a test coverage overview
    "test:coverage": "jest --coverage"
}
```

That's it! There's no cumbersome setup (although [you can tweak it](https://facebook.github.io/jest/docs/en/configuration.html#content) to fit your needs), and you can get straight to writing your tests. Boom!

## Snapshots

A huge feature that puts Jest apart from the rest is something called snapshot testing. Simply put it's a way to record a snapshot of the React component tree currently being tested, and then check future tests against the saved result. In other words - you no longer have to write endless assertions or expects, and instead can check two complete rendering results against each other. Huge time saver! You can read more about snapshot testing [here](http://facebook.github.io/jest/docs/en/snapshot-testing.html#content).

## Relevant resources recommended by the author

- [Official site for Jest](https://facebook.github.io/jest/)
- [From Mocha to Jest](https://medium.com/airbnb-engineering/unlocking-test-performance-migrating-from-mocha-to-jest-2796c508ec50)
- [Snapshot Testing](https://blog.callstack.io/unit-testing-react-native-with-the-new-jest-i-snapshots-come-into-play-68ba19b1b9fe)

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