Chapter 8. Testing

In this chapter, we’ll look at various techniques for testing your React applications. In general, we’ve found that it is a bad idea to be too prescriptive about the precise mix of tests you should have. A good guiding principle is to follow these two rules:

  • Never write code unless you have a failing test.

  • If a test passes the first time you run it, delete it.

These two rules will help you build code that works while avoiding creating redundant tests that provide little value.

We have found that early in a project, it is easier to write more browser-based tests. These tests tend to be higher-level and help capture the principal business requirements for an application. Later, when the application’s architecture starts to emerge and stabilize, it becomes easier to write more unit tests of individual components. They are faster to write and quicker to run, and once you have a stable structure to your code, you will not need to update them continuously.

Sometimes it’s worth loosening the definition of what a test is. When you are working on layout code, whose primary value is visual, you might consider a Storybook story to be a “test.” The assertion is done by your eye, looking at the component as you create. Of course, this kind of test will not automatically pick up regression failures, but we present a technique in a recipe that will allow you to turn these visual checks into actual automated tests.

If you write tests before you write code, you will find ...

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