What is unit testing?

A unit is the smallest part of a piece of software you can actually test (for example, an individual function or procedure). Unit testing is an essential step of the software testing process. Its goal is to test individual units or components of source code and validate whether each of them performs as expected.

In this article, we’d like to emphasize the importance of unit testing and recommend a couple of frameworks that will help you out specifically with JavaScript unit testing. We’ll cover the basics of testing tools such as Jasmine and Mocha and focus a bit more on Jest and Enzyme for React.

JavaScript Code - Best JavaScript Unit Testing Frameworks

Why is unit testing important?

Unit testing makes it possible to identify problems earlier on, which reduces the cost of fixing them. It also makes development faster, codes more reliable, and integration of modules easier. As a result, it reduces the number of bugs and makes the whole process less time-consuming.

Although there are some challenges to unit testing, such as needing to test doubles and finding dependencies, in the long run, tackling unit testing is definitely worthwhile.


Jasmine vs. Mocha

Jasmine was created around 2008. This free unit testing tool is a development framework designed to help you test JavaScript code. It uses behavior-driven testing and supports asynchronous specifications. Its syntax is simple and it does not require any other JavaScript frameworks nor a DOM.

Released around 2011, Mocha is a slightly newer open-source testing framework that runs on Node.js and in the browser and is hosted in GitHub. Its tests run serially, which means reporting is flexible and accurate. Other features include test coverage report, report test duration, JavaScript API for running tests, and browser support.

Some of the differences between these two are that Jasmine has a built-in assertion library and a spy framework, while Mocha does not. An upside for Mocha, however, is that it excels at BDD test definitions.

Jest and Enzyme

Jest is a testing framework created by Facebook to test JavaScript code, in particular for React apps. Meanwhile, Enzyme is a JavaScript testing utility created by Airbnb that makes it easy to assert, manipulate and traverse your React components’ outputs thanks to its great API. These two tools are your best allies when it comes to testing React applications as they’ve been designed specifically to test with React.

Jest has many benefits and features, such as the fact that it is very easy to configure, works with any JavaScript compiler and can run tests in parallel. It also includes a snapshots feature and allows you to mock any function or component as it acts as a mocking library.

You can use Jest individually, given that Enzyme just adds functionality, although we believe these tools are complementary and usually use them together. Enzyme, however, cannot be used on its own as it is not a unit testing framework. It will always need a test runner to function, which does not necessarily have to be Jest.

If you’d like more information on Jest and Enzyme and how to use them to run unit testing for React web apps, check out our previous article on this topic.

Fix and Repair - Unit Testing


There are countless tools when it comes to unit testing for JavaScript. Although we are big fans of React and have used Jest and Enzyme extensively, we also recommend Jasmine and Mocha and hope you find these tools useful in your next project.