Apple says they will not repair it, only replace it (for policy reasons), but they do not take a position on whether it would be possible to repair. I understand from other sources that a failed current checker test may have several causes, and I would hate to lose my data just because of a failed Lightning port or failed battery (rather than something more serious like a failed CPU or memory chip).
the most likely cause of a failed current checker is a failed logic board and even if they replaced that the storage is soldered on it so good bye to your data if its not backed up. and if that's the case you have no one to blame but yourself.