What is Jest?
Who uses Jest?
Why developers like Jest?
Here are some stack decisions, common use cases and reviews by companies and developers who chose Jest in their tech stack.
We are in the process of adopting Next.js as our React framework and using Storybook to help build our React components in isolation. This new part of our frontend is written in TypeScript, and we use Emotion for CSS/styling. For delivering data, we use GraphQL and Apollo. Jest, Percy, and Cypress are used for testing.
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.
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.
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.
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
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We use JUnit and Jest to perform the bulk of our automated test scenarios, with additional work with Apache JMeter for performance testing - for example, the Atlassian Data Center compliance testing is performed with JMeter. Jest provides testing for the React interfaces, which make up the backend of our App offerings. JUnit is used for Unit Testing our Server-based Apps. Mocha is another tool we use.
- 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