An important part of any application developer's life is making sure that their application runs properly the first time, every time. That can be a difficult thing to do as applications get more complicated; what might have previously required just a few minutes and a single line of code to clean up or fix might instead start taking hours, days, or even weeks (or longer) to try to fix! In addition, if you're trying to build up your application and make it work cleanly and effectively.

In this chapter, we will cover the following topics:

• The history of testing React applications
• Different ways to run React tests
• A brief introduction to Jest
• A brief introduction to the test watcher
• How to write tests