My favourite test is how well someone gives directions to where they live or work. The idiot is vague & useless, but a bright person is crystal clear & invaluable. It is a test of many things but particularly how well they can put themselves in someone else's shoes. Some are so good they'll draw you a quick map with reference points for you to navigate - this can reveal amazing spontaneous creativity. The brain-dead idiot is simply incapable of doing this.