Unit testing refers to the process of testing individual units/components of a software application in isolation. In the context of JavaScript, it involves testing individual functions or methods to ensure that they behave as expected under different input conditions.

Unit testing is an important part of software development as it helps to identify errors and bugs early in the development process. It also helps developers to ensure that their code is functioning correctly and in accordance with the requirements.

To perform unit testing in JavaScript, developers use specialized testing frameworks such as Jest, Mocha, and Jasmine. These frameworks provide tools for writing test cases, defining test suites, and running tests.

When writing unit tests, it is important to ensure that the tests are isolated from other parts of the application, and that they test only a small portion of the code. Tests should also be automated to ensure that they can be run quickly and consistently.

Overall, unit testing is a critical part of software development, and it is essential for ensuring that software applications are reliable, maintainable, and bug-free.