I was in a similar situation a few months ago and was not able to find the answer in Cactus. I needed an in-container testing framework that would help me test EJB, business logic , web services, POJOs and messaging components in my application. Also I wanted to externalize the test data from the test classes.
Finally, I wrote my framework and I am actively using it to test ejb's business logic, persistence and web services.
I have put it on sourceforge for others who might have similar needs. You can check it out at http://www.sourceforge.net/projects/marigold
There is detailed documentation on how to use the framework. Feel free to contact me (email id is on sf) if you decide on using it and have any doubts.