Acetaminophen:
"We currently want PBE to be a place where we can implement new features and make sure all the bugs associated with it to be reported and fixed before we take it live. This is much more important than testing balance, as having major bugs are very toxic to a player's experience because they might not be able to play altogether. For example, the FPS issue that everyone here helped identify by sending in their logs is much more vital than any small tweaks to a champion."
(link: http://na.leagueoflegends.com/board/showthread.php?p=16452672#post16452672)
Basicly your not going to test new champions on pbe.
-Mettalknight