I think there are four skill areas -- bidding I (using the system bids correctly), bidding II (judgment calls), declaring and defense. Some people -- and robots -- are advanced or better in some area(s) and way below in others. So grade yourself on each and then come up with an average. I suggest that for declarer play, if you've never executed a strip and endplay (like a surprisingly high percentage of the playing population) you are intermediate at best, and that if you've never executed a squeeze on purpose, you don't qualify as an expert. I'll leave it to others to suggest objective tests for the other areas.