JavaScript unit testing is essential for ensuring the quality and consistency of your software.Tests are valuable in verifying that your code functions as intended and remains stable as it evolves.It is recommended to start testing early in your development process and incorporate tests for all new work.Tests should be run continuously during development and also automated in a separate system to ensure readiness for production.Jest is a popular tool for JavaScript testing due to its ease of use and comprehensive functionality.Setting up Jest involves installing it as a dev dependency and creating tests using matchers for assertions.The Arrange Act Assert method is a common structure for organizing tests logically.Jest offers various matchers for different types of assertions to validate code behavior.Setup methods in Jest help prepare the system for testing and reduce duplication in code.Asynchronous testing in Jest is facilitated through async/await for handling processes that rely on promises.