Non regeression test in java [on hold]

i work on very big application that need to be tested. To be more specific, what is asked is to find a way to introduce non regression test. I firstly propose Junit test but after i tried to implements some test method, i realized that the scenario was hard to implements because of the high number and the heavy load of code that will be needed.

The problem with Junit is that to garantee the good execution of a functionality i have to implement multiple test method for each method used in this functionality, and this was simply to much even if i restrict myself to the sensible code of the application.

So i would like to know about the different tools/framwork that could be used to implements non regression test. I want to know about how it is done in companies to make a testing session easier for the devs, if it's automated, the adding code that will required etc...

Did some of you ever has experience in this kind of practice ?