I thought I'd take a souvaneir snapshot before I repave. The final straw was installing .NET v2.0.31112. This is the runtime you get with the beta of Monad over at BetaPlace. Installing it in a virtual machine would have been sensible, but I was impatient.
Below you can see the 'Test With... Runtime' menu. This menu is auto-populated when you install the add-in. At the moment it looks for installed versions of .NET and Mono. With some manual configuration it will work with Rotor/SSCLI as well (if anyone is interested I'll write this up as well).
The test runner used by 'Test With... Runtime' is much simpler than the one used by 'Run Test(s)'. Whereas 'Run Test(s)' will detect the test framework being used and execute a suite of tests, 'Test With... Runtime' will simply execute a single method using the specified runtime. This makes sense when you can't count on your test execution engine working on the target runtime (a serious issue when working with Rotor/SSCLI and early versions of Mono).