If you would like to know what beta testing is really about, here's a brief rundown.
(note that this is what people do who are actually testing, not just playing games.)
Create a test case, for each and every function of the emulator, in combination with every other function.
Go through them one at a time. When you get the next beta, do it again. Rinse. Repeat.
Do this often enough, and eventually all the little bugs are worked out. This is for the UI.. the games themselves, you do a similar sort of testing, but I'll tell you right now that it's a lot more complicated to test the games than the UI. You end up trying everything, even the stupid crap, in the games, to make sure it all works, even if there's no reason to suspect someone would ever do it. The only problem with testing games is that there are only 1600 or so working n64 games, so it's hard to test them all.