I couldn’t find any documentation on this so after I figured out how it works I decided to share this example. It’s really simple actually!
There’s a lot of bureaucracy when it comes to integrate game center on your game… here are a few steps…
1 – Create the leaderboards / achivements and respective IDs on itunes connect.
2 -Turn sandbox on on the iphone/ipad
go to Settings / game center/ sandbox.
3 – Create a gamecenter sandbox testing account and logging to game center.
4 – Upload the app to itunes connect and make sure to turn game center ON on and all the options needed. This will create your game center functionality on a test environment. I am not sure how much of this step is needed I only uploaded the app to itunes connect the first time and after that deploying directly to the ipad works.