I am just starting to implement OpenFeint and Game Center in my game and I'm trying to figure out how to test this stuff. I currently have OF and GC leaderboards setup and both are working, but I think I currently have them working in "release mode" and not in a testing sandbox. For example, I need to be able to reset the leaderboards and achievements in order to test things.

On OpenFeint's website I found this documentation about how to register a test user and it seems pretty straightforward:
http://support.openfeint.com/dev/test-users/

I've not been able to find any such straightforward documentation about Game Center however. Do I create a Test User under Manage Users in iTunes Connect? When I look that up I find a lot of talk about testing In-App purchases but I don't see anything about Game Center.

Meanwhile I see a button for "Delete Test Data" when I go to the Leaderboards when managing the settings for the app, but what does that do?

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ADDITION: Just found this link, hopefully reading this will help me:
https://crystal.fogbugz.com/default.asp?pg=pgWikiDiff&ixWikiPage=52&nRevision1=1

Also, I just realized Ansca fixed the bug with editing your threads. Finally!

I'm gonna test tonight or tomorrow night to see if the guess I made worked, but in the meantime I would really love to hear from anyone who knows.

Alright so I got it figured out. When you start your game and Game Center asks to login, if it's a development build the alert will say Sandbox (it appears that you must login through your app, because if you login the main Game Center app then you won't go to the sandbox.) Create a new account for testing with, don't login your normal Game Center account. And then the Delete Test Data button in iTunes Connect doesn't work instantly but will put you in a line to have the test data reset (it takes a day or two.)