Jest is a JS framework for unit tests developed by Facebook

Jest is a popular JavaScript testing framework developed by Facebook for testing JavaScript code, including applications, libraries, and other JavaScript projects. Jest is widely used in the JavaScript and React communities for its simplicity, speed, and extensive features.

Here are some key features of Jest:

1. Test Runner: Jest provides a built-in test runner that can run tests in parallel, making it fast and efficient.
2. Assertion Library: Jest includes a built-in assertion library for making assertions in tests, such as checking values, types, and behaviors.
3. Mocking: Jest has built-in support for mocking, allowing developers to easily create mock functions, modules, or entire dependencies to isolate tests and control test environments.
4. Snapshot Testing: Jest allows for snapshot testing, which enables capturing and comparing snapshots of data or UI components, making it easy to detect changes or regressions in UI output.
5. Code Coverage: Jest automatically collects code coverage information during test runs, helping developers to ensure that their tests cover a significant portion of their codebase.
6. Configuration: Jest provides a flexible and easy-to-configure framework with options for customizing test behavior, test setup/teardown, and test environment.
7. Community and Ecosystem: Jest has a large and active community of developers, and it is widely adopted in the JavaScript ecosystem. It has extensive documentation, tutorials, and community-contributed plugins and integrations.

Jest is compatible with various JavaScript frameworks and libraries, including React, Angular, Vue, and Node.js, making it a versatile choice for testing JavaScript applications across different environments. Its focus on simplicity, speed, and ease of use has made it a popular choice for many JavaScript developers for writing and running tests to ensure the quality and reliability of their JavaScript code.