What is Jest? Jest is an open source library for testing JavaScript code, maintained by Facebook. It’s more than another testing solution — It’s the complete package. It provides everything out of the box, from unit to front-end browser testing. You don’t need to add additional assertion libraries, mock functions or services.
Let me walk through a handful of reasons why you might consider migrating from another JavaScript test solution to Jest.
Comparison
The Jest implementation is well-suited for React applications, although it can easily integrate into other JavaScript applications. It’s very fast and easy to use. It's a one-stop shop, in my opinion, allowing you to develop several types of tests because of its compatibility with other modules. This post can’t cover all of the available JavaScript solutions, but the table below provides insight into a handful of solutions that can help you test multiple types of tests.
Test Type | ||||
Unit | X | X | ||
Integration | X | X | X | |
Visual | X | X | X | X |
Front-end | X | X | X | X |
My team and I have been using NightwatchJS for a couple of years. After comparing a few other test solutions, it’s time for an improved solution — Jest. (If you’re not using it, give it a try.)
As developers’ ownership of quality continues to shift to adding more and more tests, my team has wanted a solution that caters to their needs. Jest allows developers to write unit, integration, visual, front-end browser, and performance tests. Jest and Mocha are very similar. Mocha requires a lot more configuration, but is a well-established solution with many more integrations available. Jest, however, usually works out of the box with zero configuration.
Strengths and Robust Feature Set
Jest has a feature-rich API library for testing which is continuously being developed. It’s a well-documented solution with a number of guides to help with on-boarding. The documentation also allows for easy browsing.
In addition:
It's fast, compared to the other solutions mentioned above
If you're into visual testing, it can perform snapshot testing. (My team is working on developing an Applitools library.)
It automatically handles splitting of tests across processes by taking a round-robin approach to squeeze the most out of your processing power and maximize performance.
Zero configuration on most JavaScript projects, and everything you need out of the box.
No additional setup required. You're able to generate code coverage information by adding the coverage flag from the command line (includes untested files).
Easy mocking that allows you to test functionality that depends on the database, network requests, access files, any external system, or that lets you spy on the behavior of a function.
Conclusion
Jest is everything you dream of from a single solution for developers: readable test syntax, tests that run faster, quicker turnaround time during development, and more. That's why I think it's one of the best testing solutions available today. Happy testing!
Greg Sypolt (@gregsypolt) is a senior engineer at Gannett and co-founder of Quality Element. The last 5 years focused on creation and deployment of automated test strategies, frameworks, tools, and platforms.
