No hacking for the F# unit test anymore. I just published the F# unit test template for Visual Studio 11. Now you can create F# unit test project and add new unit test item. You will get something like the following screenshot when you click "Unit Test", "run unit tests", and "All tests".
Personally I have a small library for my own unit test authoring to save some typing when I write my unit testing. Feel free to leave comment.
Be sure to make your test case return "unit", otherwise it won't be recognized as a test case.