Well first off, I’m not very good at having OOBE’s, and I barely had one.
This thought just randomly came into my head, since alot of people think OOBE are just glorified dreams, someone should like put a sign with a word on it, facing the opposite direction from the person sleeping. And the person who put it there somehow doesn’t know what it says, neither does the the sleeping. Then the person gets out of their body (Assuming they’re good at this, and can do it on command) and reads the sign, and wakes up and records what he read. Then checks it in real life, and if they match, it proves that they’re legit. It could be repeated a few more times to make sure the results are reliable.
Sounds interesting, I would like to see what the results will be! 
I’d be interested in the results as well- my idea of (lucid) dreaming is a very scientific one, therefore I don’t think OOBEs are impossible, but I’d like to have more hints than just memories. If OOBEs are more than dreams, it must be possible to proof this. As far as I know nobody could do this before, and there is no sleeplab data about all this.
The most common test is to take a playing card without looking at it and place it somewhere and look at it during and OBE. I’ve only had one OBE but I am planning to test it sometime. Robert Bruce, a famous OBE-researcher, says its about 70% you get the card right varying a lot from person to person. I think it’s not 100% because the SC can interfere.
Even if its not really outside of our bodies, its an awesome journey 