"Testing code is the first step to making it secure, and using unit tests ensures that each smaller function within an app behaves as it should." The primary purposes of unit tests include verifying functionality, preventing code regression, documenting code, securing apps, and scoping and writing unit tests. To write a unit test, one should keep tests short and simple, consider both positive and negative test cases, break apart long and complex functions, avoid network and database connections, and use mocking to simulate real-world interactions. The Mocha Framework is used in this tutorial, which guides the reader through creating a new project, implementing a class, configuring and adding unit tests, and running the tests. With unit tests, developers can catch bugs early, prevent code regression, document their code, secure their apps, and refactor and optimize their code without worrying about behavior."