The IncludeTestAssembly property doesn't seem to appear anywhere on learn.microsoft.com, which makes it difficult to use correctly. At a minimum, I think it needs to be mentioned in these two places:
There may be other places as well, but these are the two that you can directly reach from https://learn.microsoft.com/en-us/dotnet/core/testing/unit-testing-platform-extensions-code-coverage#microsoft-code-coverage.