An Introduction to Jest JavaScript Testing Framework

An open source testing toolkit that works on most JavaScript projects

The topic for today is Jest, a JavaScript testing framework which comes in handy for testing your JavaScript projects. At the time of this writing, it comes with great support for Babel, TypeScript, Node, React, Angular, Vue, and a lot more.

According to the official documentation, it provides the following functionalities:

• fast and safe
• code coverage
• easy mocking
• great exceptions

Jest is a great testing toolkit for developers who are looking for other alternatives and have experience with the following testing frameworks:

• AVA
• Expect.js
• Jasmine
• Mocha
• proxyquire
• Should.js
• Tape

Let’s proceed to the next section and start installing Jest.

testing jest javascript programming

Here I show how to test your Javascript code. We will test pure functions (they are the easiest to test, because they don't have side effects). Then we test a function with side effects and we mock a global function using Jest. And finally we test an object method. We also talk about AAA (Arrange Act Assert) pattern here.

As a developer, I know for a fact that I have to constantly brush up myself with new updates. This means that not only I have to keep learning more about the frameworks and language I work with but also to look for new frameworks that gives me an edge over others. One such survey that I am always looking forward to as a developer is the ‘StateofJS’. It is revered by all the JavaScript developers as a key source of information. ‘StateofJS’ provides key insights on the major trends in front-end, back-end, testing, etc. As per StateofJS 2019, Jest has been the most interesting and satisfying framework for JavaScript testing.

In this Jest tutorial for beginners, you'll learn how to getting started with JavaScript unit testing with Jest framework. What means testing? How to test JavaScript code with Jest? Learn the basics of testing JavaScript with this Jest tutorial for beginners!

I use Jest nearly every day when working, and it's a fantastic tool. It lets me ship my code with confidence, knowing that I have produced something which works as intended.

Ensure the stability of the JavaScript code in your WordPress plugin by writing JavaScript unit tests using Jest. WordPress has a long record of unit testing its PHP code. However, writing JavaScript unit tests and integration tests for the code in themes and plugins doesn’t enjoy the same status. Let’s see how to test the JavaScript in our WordPress plugins and themes using Jest.