Jest is a JavaScript testing framework developed by Facebook, designed to simplify the process of writing and running tests for JavaScript applications, particularly those built with React. With features such as snapshot testing, mocking, and code coverage reporting, Jest enables developers to write  and reliable tests for their JavaScript codebases. Developers can learn how to use Jest to write effective unit tests, integration tests, and end-to-end tests for their applications, ensuring code quality and stability throughout the development lifecycle.

Jest

With Jest 26 we are shipping a new implementation of fake timers based on @sinoners. Jest is now 4 MiB smaller than Jest 25.5.4 (53 → 49 MiB) Jest's own size was reduced by 1.2 MiB (4.3 -> 3.1 MiB).

Jest 26: Tick Tock