Jest is a popular JavaScript testing framework designed for ensuring the correctness of code. It is widely used in the development of web applications, particularly those built with React. Jest provides a simple and intuitive API, making it easy for developers to write and run tests. One of the key features of Jest is its ability to run tests in parallel, which speeds up the testing process. It also includes built-in mocking capabilities, allowing developers to simulate functions and modules. This helps in isolating tests and ensuring that they focus on specific parts of the code.