Finding a reason to echo someone's own opinion back at them after a suitable time where they've forgotten they voiced it is a very effective test for disagreeableness, I've found. You don't need to chase them down about the contradiction. Just note it and take appropriate future actions.

It can even be a bit amusing, if they are insulting about it, to watch them vigorous call themselves stupid for expressing their previous opinions.

I find many of my previous positions to be stupid.

Right, as should we all. The key question is, when you're confronted with one of those opinions, do you defend it, deny it, or renounce it?

Agreed - and you will find not a single living person will pass this test over time. Therefore, it's a worthless, but deeply amusing, test. Human ignorance is so pervasive it even applies to people like you :)

I can tu quoque right back at you; can you conceive of a person who expresses some opinion (and this includes technical matters, things within the scope of your job, opinions you are being paid to have, not just random political things) only and solely because it is their real opinion? No, if you came at with me with my own opinion two weeks later, you would not find I have radically shifted very often, and even less often without realizing I've shifted, and virtually never insulting whoever held the opinion I held two weeks ago.

I don't base my opinions on whether or not I get to contradict someone else. Clearly some people do.