Given the enormous expansion dbatools is seeing, adopting ANY automated test facility adds value. Tons of pages have been written about how to correctly test code, from pieces to full apps. Take a quick google search on "unittests", "integration tests", "regression tests", "behavioural tests", "pragmatic testing" to be overwhelmed with options and opinions. This is by no means a complete guide, but just a reminder for newcomers wanting to contribute to dbatools testing, now that "appveyor via pester" recently came into play.
In a large module like dbatools, offering all kinds of features in a wide range of environments (a quick