JRE Testing Effort

My client is planning a JRE upgrade, and wants to know the extent to which other accounts have tested their applications.  Would the standard CPU testing process suffice or is more rigorous application testing required?  Do we need to test every function on every form or or should we simply check to make sure that forms launch?  I know this is a general question, and we all have our opinions, but I would like to find out more about other people's testing experience with the transition from Jinitiator to JRE.  Thank you.