There is a wise saying which states that if you want to know a man's character, give him power. I would add that it is enough to just give the illusion of power and that would be enough. And, as bad as it sounds, money, power, status, are all great ways to test people. Friends and family included.
I think it is better to know when you deal with such a person and admit it, first to yourself. People can say all sorts of stuff only to deny the reality: brown is brown, there is no use putting a pink ribbon on top.