If you're interested in using F# for testing, you may be interested in this Mark Seemann lecture about TDD in F#, turns out it's well suited for writing unit tests, even unit tests for other .NET languages:

http://www.infoq.com/presentations/mock-fsharp-tdd

Mark Seemann also has a F# Unit Testing course on Pluralsight if you're interested in applying this in practice (Pluralsight is awesome by the way, it's not free but if your company can afford it I can definitely recommend it, especially if you use Microsoft products in your tech stack):

http://www.pluralsight.com/courses/fsharp-unit-testing

I tried using F# (FsTest, specifically) for testing. It's great to be able to write verbose test names with double-backquote syntax, that way your test cases read in English instead of this_ugly_underscore_based_sentences.