Drupal Testing Strategies
Philip Norton, #! Code, Jun 26, 2022
https://www.hashbangcode.com/article/drupal-testing-strategies
Inventory of tools for static analysis, code sniffing, load testing, and unit testing.
Testing plugins section in: Drupal 9: Adding Custom Plugins To The Session Inspector Module
Philip Norton, #! Code, Mar 6, 2022
https://www.hashbangcode.com/article/drupal-9-selecting-machine-names-content-entities-and-fields
The article is not about testing but contains an example of testing plugins.