I'd like to create a new fixture type in the .NET flavour of FitNesse, similar to Fabrizio Cannizzo's RestFixture, which is written in Java. RestFixture can be used with both FIT and SLIM and I would like my .NET version to also work with both FIT and SLIM.
In FIT it's possible to create a new fixture type in .NET since the fixture classes are defined in the .NET test runner, FitSharp, and they can just be extended. However, I understand that in SLIM the fixture classes are included in FitNesse, not in the test-runner, and FitNesse is written in Java. So does that mean we can't create new fixture types for SLIM in .NET?
If it is possible to create a new fixture type for SLIM in .NET, how can I do it?
Your understanding is correct. SLIM fixtures can only be written in Java. This is one of the limitations of SLIM (or benefits, depending on your point of view!)