This article is the 3rd part of a series about Roslyn Source Generators & co. In the 1st article, of this series, we built an Incremental Source Generator to generate a new property Items of a Smart Enum. In the 2nd article, we added a Roslyn Analyzer and a Code Fix to prevent common mistake(s) and to help out the developers when using this Source Generator. All the code we have written so far was tested manually by executing the code and looking at the outcome. It is time to implement some automated tests to ensure the correct behavior.