The removed test is not marked for execution and was done when I had little understanding of properties testing.

Now I'm perfectly able to doing it in proper way :), as done e.g. in this two projects:
https://github.com/gsscoder/csharpx
https://github.com/gsscoder/sharprhythm

Anyway when I addFsCheck.Xunit to test project (without any other change) a lot tests get broken!

I'll do further investigation for this strange thing... For now better remove useless code even from test codebase.