Eugene, have you considered adding GrailsAwareInjectionOperation to the compiler for Grails projects?
I have been working a javaagent/classloader that bootstraps Grails via a JUnit4TestRunner and dynamically compiles Domain artefacts so they can be tested interactively. It is quite easy to bootstrap grails with a mock MockServletContext, but getting the classloader to work just right is quite complicated. I'll post the details some other time, but I will say now that I have it all working except the Domain class loaded in the unit test turns out to a different instance loaded elsewhere. But even should resolve this last problem, its a shame to have idea do all the work of compiling only to have "grails test-app" do it all over again only to run a single test.
If jetgroovy were to simply to configure compilation units like below, we would be able to test grails apps directly within Idea. Its not enough to have pleasure in coding groovy/grails, testing must be pleasurable as well!
Of course, the integration would need be flexible, not how I hard coded it below.