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Assess
Jest is a JavaScript testing framework by facebook to test JavaScript code and React applications / components.
We started using Jest (and watchmen) instead of Karma because it:
- gives us integrated mocking library
- gives us integrated support for testing "promises"
- gives us integrated code coverage report
- automatically runs tests related to changed files (instead of all tests)
- gives us parallel test execution
- gives us snapshot testing for React components
It is easy to set up. And even if you have a running setup with Karma/Chai you can easily replace Karma with Jest. With a small workaround, Chai and Jest test matchers work fine together.