I have made good progress integrating Hk2 injection inside JUnit tests so I have written a wiki page on how to better unit test your modules with JUnit and Hk2.
http://wiki.glassfish.java.net/Wiki.jsp?page=TestingWithHk2
Now you can use @Inject inside junit tests and have habitat services injected and tested. It should simplify the testing of individual modules, please try to use this as soon as possible for unit testing.
I believe we should be able to do the same with TestNG but I have no cycles for that, if anyone wants to pick that up, it would be great...
jerome