How to test GameCenter Achievements before publishing?

I'm adding GameCenter Achievements to my game:

          
Code Block
let a = GKAchievement(identifier: "levelcomplete2");
a.percentComplete = 100;
GKAchievement.resetAchievements() { (e) in
print("ERRORA: \(e)")
}
GKAchievement.report([a]) { (e) in
print("ERROR: \(e)");
 };


The error shows "nil" but because the Achievement isn't live yet (the App is not published), there's no success-banner showing in the app. How can I test if it's working?

Did you ever find an answer to this question?!

How to test GameCenter Achievements before publishing?
 
 
Q