Implement validation tests

Fixes for test failures added

All tests pass now

For more information about the changes in ba662d58 see the following for more information:
Avoid using constructors in extended plugin classes:
https://www.previousnext.com.au/blog/safely-extending-drupal-10-plugin-c...
https://www.drupal.org/node/3468511 →
https://www.drupal.org/node/3076421 →

Assigning entity storage to a property instead of the entity manager:
https://mglaman.dev/blog/dependency-injection-anti-patterns-drupal

Moved the last two commits to separate issues so they can be further evaluated/tested/expanded upon
📌 Safely extend plugin classes Active
📌 Code quality fixes Active

Automatically closed - issue fixed for 2 weeks with no activity.