Kernel tests
Kernel tests are the immediate higher-level testing methodology we can have in Drupal and are actually integration tests that focus on testing various components. They are faster than regular Functional tests as they don't do a full Drupal install, but use an in-memory pseudo installation that is much faster to bootstrap. For this reason, they also don't handle any browser interactions and don't install any modules automatically.
Apart from the code itself, Kernel tests also work with the database and allow us to load the modules that we need for running the test. However, unlike the Functional tests we will see next, Kernel tests also require us to manually trigger the installation of any database schemas we need. But we will see how we can do this in the two examples we cover in this section.
Before we can work with Kernel tests, though, we need to make sure we have a connection to the database, and PHPUnit is aware of this. Inside the core folder...
