To summarize, the async feature works under NUnit built for CLR 2, of course it will use an agent to run tests built for CLR > 2. There is a sort of infrastructure problem that I posed already which concerns how to build and test the async thing. Currently I didn't make any explicit choice and the build fails if you try to build for CLR < 4, because it tries to build the .NET 4.5 test assembly. So far therefore you can successfully run a build with net-4.0, which will run the new tests as well. Of course I also ran them under NUnit built for CLR 2 but it's a manual process: exclude the tests from the build, build for CLR 2, invoke nunit-console.exe (CLR 2) on the 4.5 assembly previously built. Ideally we would have to come up with a way to say that even when we build for < 4.5 (there's no 4.5 now but only 4.0 as NAnt doesn't support it yet), that assembly is still built for 4.5 so that tests can be run on it with NUnit built for .NET < 4.5. I hope it makes sense. I would like to clarify this with Charlie. Also one question for Charlie: in order to see if tests are run correctly I created some fixtures which are not supposed to be run directly but via my own test code. In order to accomplish that I marked the suite as ignored, but those tests then end up in the build results as ignored, which is not really the case 'cause I'm running them by some other means. I wanted to figure out if there was a way to make NUnit /ignore/ those tests so that they don't show up as ignored. Simone On Tue, Oct 2, 2012 at 9:34 PM, Charlie Poole