Well in Buddhist teaching, in some traditions anyway - if you are enlightened then you see all other beings as enlightened too. So - one test to see if you are enlightened yourself might be to ask if you know anyone who is unenlightened. If so then you are not enlightened yourself :).
So, really, you can't test to see if others are enlightened, like that. The thing is, that all our tests, and space and time themselves are part of the illusion that you wake up from when you become enlightened.
And though we may look around the world and see tyrants and evil people - how could anyone see them as Buddha? But what we see is very limited, just one time slice, into countless trillions of lifetimes (if you think that way at least, though that's also part of our limited ways of looking at the world), and Buddhas are not limited in that way.
And according to the teachings, everyone, without exception, has the capability to be enlightened, and their enlightened nature is only slightly obscured, if only they knew it, indeed the obscuration, even of the most evil tyrant, though they are so caught up in their delusion that they can't see it, is actually unsubstantial to the extent that if you try to pin it down, you can't find it at all.
And an enlightened person can manifest in any form, and may do things that seem crazy, and may make mistakes. He doesn't care, has nothing to lose, nothing to prove to others, if some crazy seeming action benefits others, well he or she'll just go ahead and do it.
(In this wherever I say "He", means "he or she" of course).
Sometimes for instance it can be of most help to others to let them see examples of what not to do, and how badly things can go wrong if you make mistakes.
For as long as we are caught up in the illusions of samsara, the way we see the world simply doesn't permit us to see someone who is fully enlightened. If a fully enlightened Buddha stood in front of me, all I could hope to see is an ordinary chap like myself, with flaws like mine, and problems and personal issues and physical disabilities and so forth.
You wouldn't expect him to be able to work miracles, to fly, to walk through walls, all the crazy things that people sometimes say you can do if you are enlightened. But, though you do get stories like that in the old tales about enlightened beings of the past - those don't really show that you are enlightened either, if anyone was able to do things like that.
Especially in our modern world, if that was possible, they'd just get a whole lot of puzzled physicists trying to measure everything and work out how you did it, and trying to figure out what new physical laws to invent to explain it all. I don't know if an enlightened being could do miraculous things like that in our modern scientific world, but if he or she could, then I'd be surprised if they'd find it a compassionate thing to do, given the amount of angst and worry it would cause to most people to see such things disrupting their cozy view of the world.
One of the main things about it is - that he is not in any way acting to bolster himself and create a position or place for himself, or herself in the world. Has gone beyond all those games. Has no need to do that.
Indeed - that idea has kind of easy to see aspects to it, e.g. if someone claims to have spiritual powers, when he or she doesn't, or goes around making a big thing about some minor insight they have - that's likely to block any future understanding they might otherwise have been able to have.
But it also has more subtle aspects - and though you get rid of the worst types of self sustaining and boosting activity as a bodhisattva on the path, in the mahayana tradition, you don't really, completely, get rid of all that self boosting totally, until you are Buddha. Until then you are still making distinctions that hold you back, subtle ones perhaps, yet very strong, stronger because they are hard to spot.
At some point though you finally let go of it all. Best to say what that's like in the Buddha's own words, at least, according to the stories, and legend, when he became enlightened, he said
Through the round of many births I roamed without reward, without rest, seeking the house-builder. Painful is birth again & again.
House-builder, you're seen! You will not build a house again. All your rafters broken, the ridge pole destroyed, gone to the Unformed, the mind has come to the end of craving