Testing is something that's absolutely critical to the overall health of your application! It ensures your development cycles are sane and your deploys are not incredibly dangerous. Your behavior can be tested, verified, and you can be confident in what your application is doing at any point in time without ever needing to open up a browser!
This is something that used to be a nightmare to do. The React test setup was a function that people generally hated given how much of a time commitment it took and how finicky it ended up being after the setup was done. One misstep or bad configuration change and the entire test harness framework could fall apart completely!
Be prepared to write a lot of tests if you write a production-ready React application! It's a great software engineering practice to be do whenever you're doing anything code-wise, and React is...