4.2 Demonstrate ability to develop Custom Modules using Drupal API for extending Drupal functionalit
Review how to call the correct base Class. Review Drupal core's file pathing to kernel tests.
In core, the PSR-4 'tree' starts under core/lib/. https://www.drupal.org/docs/develop/coding-standards/object-oriented-code
The ControllerBase is a utility base class for thin controllers. This is used to load pages/controllers. Drupal 8 uses the Symfony HTTP kernel system to request and produce a requested object - a response object to send back to the client. Read more on Drupal.org's Underlying functionality of the routing system in Drupal 8
The FormBase provides a base class for forms. The Drupal form api handles the creation, submission and validation of a form.
The ConfigFormBase is the base class for system configuration forms. Configuration forms are used to get and set data entered by a user. Read more on Drupal.org's Working with Configuration Forms.