The last few days I've been hacking away at getting something up and running that fits into the Eclipse JUnit UI. Unfortunately, the events that are being reported by GrailsBuildListener are not sufficient. The UI needs to get a copy of the test-tree before the tests start executing (so the test view can be populated).
I have hacked-up something that modifies the TestApp and _GrailsTest scripts in Grails 1.3.4 to be able to get these events.
The good news is... I was able to get something going that "sort of works". The bad news is that I'm not sure if it doesn't in some way break the test running scripts. I haven't got good projects with realistic test suites to try it out on. I've had to make some changes to the ordering in which things get prepared and executed (which is a bit scary with all the state mutations and implicit context dependencies in the Gant scripts).
I'll attach the modified scripts here, maybe someone on the Grails team can have a look at them and give me some feedback.
PS: I also had some issues with classpath and classloaders to get the BuildListener implementation I made loaded up AND able to access the classes it needs (like Suite class from JUnit4) without classloader constraint violations.