Notification spy (source: http://blog.bignerdranch.com/729-notifications-part-2-handling-and-spying/)

NotificationSpy

NSNotificationCenter *center;
center = [NSNotificationCenter defaultCenter];
token = [center addObserverForName: nil
                object: nil
                queue: nil
                usingBlock: ^(NSNotification *notification) {
                    QuietLog (@"NOTIFICATION %@ -> %@",
                              notification.name, notification.userInfo);
                }];