The rule test manager is intended to be in the 4.1 or 4.2 release, and initially be integrated with the BRMS (but there is no reason why it can't be integrated with the IDE at a future date).
Rough features (still have to scrape them off Mic's whiteboard):
Be able to select a rule to focus on
Can chose to NOT fire actions (ie if action does something destructive, - just want to check the rule activates correctly).
assertions on result data
be able to have simple expressions to init data (?) or analyse results (?)
JUnit integration (?) - how?