As your programs or web applications become more complex, you'll want to test them to make sure that new changes don't break their original functionality.
In the Quality Assurance Certification, you'll learn how to write tests with Chai to ensure your applications work the way you expect them to.
Then you'll build a chat application to learn advanced Node and Express concepts. You'll also use Pug as a template engine, Passport for authentication, and Socket.io for real-time communication between the server and connected clients.
Text by freeCodeCamp https://www.freecodecamp.org/learn/quality-assurance