The Karma you get for not using Jest (2024)

What is Jest?

Jest is a JavaScript testing framework designed by Facebook to make JavaScript unit test execution simple. It has multi-framework support, and can be used with Angular, React, Vue.js, Node, etc.

The focus of this article will be on Angular.

What is Karma?

I’m sure everyone who has worked with Angular knows what Karma is. To refresh, Karma is the unit test framework created by the original AngularJS team that is pre-installed when you install Angular.

Why use Jest over Karma?

With my experience using Karma, I found it very slow to work with because of the time it takes to launch and load the web browser then execute every unit test.

The benefits for using Jest and Karma are:

Faster unit tests: Since Jest is a browserless testing framework, it takes a lot less time to run the unit tests. Comparing test execution time, I found that Jest runs unit tests at 2x to 3x the speed of Karma. This can be drastic as your project becomes larger and the amount of test cases skyrocket.
Easy configuration: Jest is advertised to be the framework that works out of the box. Just download it and run it. Although for my project I did have to make configurations (since the application I’m working on is relatively complex in structure), for majority of projects it runs perfectly after download.
Easier CI/CD integration: Even though Karma has CI/CD support for several products, it requires some configuration and it doesn’t support every CI/CD product. It was impossible to use Karma with Bamboo (Atlassian CI/CD server). Fortunately for Jest, since it just runs inside the command line, it is easy to integrate with every CI/CD pipeline.
Jest can be easily used with Jasmine: When I made the change from Karma to Jest, I feared that I would have to change how I wrote my unit tests to accommodate this switch. Thankfully, all my unit tests ran perfectly.

How to switch from Karma to Jest

Run the following commands in Command Line to replace Karma with Jest:

> npm install jest @types/jest --save-dev
> ng add @briebug/jest-schematics

Note: If you have libraries installed in your project that’s not from node_modules. You must add the following in your packages.json file:

"jest": {
 "moduleDirectories": [
 "node_modules",
 "lib"
 ]
}

Running Jest

Now you can run the following command to run unit tests with code coverage:

> npm test -- --coverage

Takeaway

The purpose of this is to free more time for developers. If you make this transition from Karma to Jest, it will bring back great rewards in terms of easy integration and unit test execution speed. This allows you to continue to deliver excellent and efficient products!

Hope this helps!