In this chapter, we talked a bit about automated testing in Drupal 8. We started with an introduction about why it's useful and actually important to write automated tests, and then briefly covered a few of the more popular types of software development testing methodologies.

Drupal 8 comes with advantages in this field over its predecessor by integrating with the PHPUnit framework for all the different types of testing it does. And there is a capability for quite a lot of methodologies as we've seen exemplified. We have unit tests—the lowest level form of testing that focuses on single architectural units and which are by far the fastest running tests of them all. Then we have Kernel tests which are integration tests focusing on lower level components and their interactions. Next, we have Functional tests which are higher level tests that focus on interactions with the browser. And finally, we have the FunctionalJavascript tests which extend on the latter and bring Selenium and Chrome into the picture to allow for the testing of functionalities that depend on JavaScript.

We've also seen that all these different types of tests are integrated with PHPUnit so we can run them all using this tool. This means that all the different types of tests follow the same "rules" for registering them with Drupal, namely, the directory placement, the namespacing, and the PHPDoc information.

The world of automated testing is huge and there can be no single chapter in a book that can cover all the different ways something can be tested. For this reason, especially for beginners, the journey towards good test coverage is full of trial and error when reading Drupal and PHPUnit code and documentation, and even has the occasional frustration. But out of this, we get stable code that works always and that is protected from regressions.