What is Jest?

Jest provides you with multiple layers on top of Jasmine.
Jest is a tool in the Javascript Testing Framework category of a tech stack.
Jest is an open source tool with 26K GitHub stars and 3.5K GitHub forks. Here’s a link to Jest's open source repository on GitHub

Who uses Jest?

Companies
260 companies use Jest in their tech stacks, including Airbnb, Facebook, and Instagram.

Developers
148 developers use Jest.

Why developers like Jest?

Here’s a list of reasons why companies and developers use Jest
Jest Reviews

Here are some stack decisions, common use cases and reviews by companies and developers who chose Jest in their tech stack.

Eli Hooten
Eli Hooten
CTO at Codecov · | 14 upvotes · 13.9K views
atCodecov
Jest
vuex
Python
Vue.js

We chose Vue.js at Codecov to replace a front end that was based mostly on server side rendered Python templates, and was getting fairly long in the tooth. The move to Vue.js allowed us to take a more component driven approach to our front end, providing greater flexibility and reuse when creating new pages and refactoring old ones. Another bonus was how easily we could integrate Axios with VueJS for making AJAX calls within Vue.js components and their associated vuex stores. We were also able to easily integrate Vue.js with the Jest testing framework, which allowed to provide test coverage for a front end where none previously existed.

The move to Vue.js has allowed us to be more agile in our front end development by further decoupling our front end from our back end. Additionally, by fully embracing a component-driven approach, we're able to more easily isolate and test functionality, leading to a more readible, maintainable, and extensible front end codebase.

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Jest
redux-thunk
React
Redux
redux-saga

Choosing redux-saga for my async Redux.js middleware, for a React application, instead of the typical redux-thunk .

Redux-saga is much easier to test than Redux-thunk - it requires no module mocking at all. Converting from redux-thunk to redux-saga is easy enough, as you are only refactoring the action creators - not your redux store or your react components. I've linked a github repo that shows the same solution with both, including Jest tests.

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Russel Werner
Russel Werner
Lead Engineer at StackShare · | 7 upvotes · 17.4K views
atStackShare
Percy
Happo.io
React Storybook
Enzyme
Jest

We use Jest because when we rebooted our "front end" stack earlier last year, we need to have a testing solution (we didn't have any front-end tests before that!). Jest is fast and convenient and it has plenty of community support behind it. It let's us run our unit tests with Enzyme and snapshot tests.

This is an area that we are constantly reviewing to see what can be improved, both in terms of developer needs, accuracy, test maintainability, and coverage.

I'm currently exploring using React Storybook to be the record of snapshot tests and using some online services, such as Happo.io and Percy in our CI pipeline.

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Dschinkel Schinkel
Dschinkel Schinkel
Enzyme
React
JavaScript
Jest
Mocha
#Testdrivendevelopment
#Bdd
#Tdd

I use both mocha and Jest because:

  • I don't care whether teams use Jest or Mocha. But jest is way too overhyped. Most devs are writing integration tests and think that it's so much better but frankly I don't write integration tests as the way to get both design feedback and confidence when I code. I adhere to the test pyramid, not ice cream cone or the dumb "trophy"

  • I TDD, so I only ever use the "API" of test frameworks. I don't do a lot of integration tests for TDD and all the bells and whistles Jest provides you from the command-line I just don't need. And I certainly do not care about or touch Jest Snapshots, I despise them

  • My tests are fast enough because I write isolated tests with TDD, so I don't run into performance issues. Example: I write my tests in a way that I can run 300 tests in literally 1 second with mocha. So the Jest ability to pinpoint and only run those tests which are affected by code changes. I want to run all of them every time when I TDD. It's a different mindset when you TDD

  • I also mainly code in IntelliJ or WebStorm because I feel the tools in that IDE far surpass VSCode and I also love running the test UI runner in it vs. lousy command-line

  • I feel both mocha and Jest read just fine in terms of code readability. Jest might have shorter assertion syntax but I don't really care. I just care that I can read the damn test and my tests are written well and my test descriptions, as well as the code itself including constants represent business language, not technical. I care most about BDD, clean code, 4 rules of simple design, and SOLID

  • I don't like using mock frameworks so no I don't use Jest's Mocking framework. I don't have to mock a lot in my tests due to the nature of how I strive to code...I keep my design simple and modular using principals such as clean code and 4 rules of simple design. If I must mock, I create very simple custom mocks with JS

  • On the contrary to the belief that integration tests and mount are the way to go (this belief drives me absolutely crazy, especially Dodd's promoting that), I TDD with shallow & enzyme. My tests are simple. My design is driven by my tests and my tests give me quick and useful feedback. I have a course I'm working on coming out soon on TDD with React to show you how to truly test the FE and why the ice cream cone and trophy suck (you're being scammed people). Watch for that here: https://twitter.com/DaveSchinkel/status/1062267649235791873

Don't forget to upvote this post!

Mocha Jest JavaScript React @jsdom Enzyme #tdd #bdd #testdrivendevelopment

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Scott Mebberson
Scott Mebberson
CTO / Chief Architect at Idearium · | 2 upvotes · 14.9K views
Jest
Mocha

We used to Mocha for as our primary Node.js test framework. We've now switched to Jest and haven't looked back.

Jest is faster and requires less setup and configuration. The Mocha API and eco-system is vast and verified, but that also brings complexity.

It you want to get in, write tests, execute them and get out, try Jest 😀

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Lars Lockefeer
Lars Lockefeer
Mobile Tech Lead at Picnic · | 2 upvotes · 4.8K views
atPicnic
Prettier
Jest
React Storybook
styled-components
CodePush
RxJS
Redux
TypeScript
React Native

Earlier this year, we started developing a new app to help our runners deliver groceries to our customers. We chose React Native over a native app or a PWA and are really happy with it. So far, we really like what we are seeing. Development speed is fast and the tooling is awesome. The “learn once, write anywhere”-promise is really fulfilled and when we ran our project for the first time on iOS after a few weeks of development, we were excited to see how well it worked and what it looked like.

Read our blog post to learn more about how we use React Native, TypeScript, Redux.js, RxJS, CodePush, styled-components, React Storybook, Jest, and Prettier to develop this app, as well as our thought of what else we will do with it at Picnic.

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Jest's features

  • Familiar Approach: Built on top of the Jasmine test framework, using familiar expect(value).toBe(other) assertions
  • Mock by Default: Automatically mocks CommonJS modules returned by require(), making most existing code testable
  • Short Feedback Loop: DOM APIs are mocked and tests run in parallel via a small node.js command line utility

Jest Alternatives & Comparisons

What are some alternatives to Jest?
Mocha
Mocha is a feature-rich JavaScript test framework running on node.js and the browser, making asynchronous testing simple and fun. Mocha tests run serially, allowing for flexible and accurate reporting, while mapping uncaught exceptions to the correct test cases.
Selenium
Selenium automates browsers. That's it! What you do with that power is entirely up to you. Primarily, it is for automating web applications for testing purposes, but is certainly not limited to just that. Boring web-based administration tasks can (and should!) also be automated as well.
AVA
Even though JavaScript is single-threaded, IO in Node.js can happen in parallel due to its async nature. AVA takes advantage of this and runs your tests concurrently, which is especially beneficial for IO heavy tests. In addition, test files are run in parallel as separate processes, giving you even better performance and an isolated environment for each test file.
Jasmine
Jasmine is a Behavior Driven Development testing framework for JavaScript. It does not rely on browsers, DOM, or any JavaScript framework. Thus it's suited for websites, Node.js projects, or anywhere that JavaScript can run.
Enzyme
Enzyme is a JavaScript Testing utility for React that makes it easier to assert, manipulate, and traverse your React Components' output.
See all alternatives

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