zk app unit Testing

I have an app developed with zk. Its composed as 3 modules : GUI project(UI zul page, comptroller, ejb lookup DAO for each Ji) common project(common utility classes exist), ejb project (where we place all our transaction pieces). We need to start with unit testing. My question , how to start with. Knew with jUnit,selenium and some zk supported testing tool. 1. My UI operation connects to ejb module for DB operations which basically all screens as well user operation ends with. How to start with these scenarios. Controller part listens for event handling, sets some page/session attribute, does some validation and throws 'WrongValueException' on the Ji components.....