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...