Back in Chapter 5, Testing and Debugging Your Server, we did unit testing for our Node code, and we used Jest for it. As we said there, an advantage of this package is that we can also use it with React (or React Native, which we'll be looking at in Chapter 11, Creating Mobile Apps with React Native), so everything we learned about earlier in this book still holds; give it a quick look over if you will, so we won't have to repeat ourselves here.
What shall we test? Obviously, we'll have to write unit tests for our components, but since we've been using Redux, we'll also require tests for reducers, actions, and thunks; we'll cover all of these topics in this section and the following ones. Some of these tests will be quite simple to write, and for others, some more work will be needed. Let's get started...