It has to be testing for how consciousness is created, I mean, it's as "easy" as just poking around inside people's brains until they start to experience weird stuff. They've even found a "consciousness off switch", but apparently there hasn't been any more discoveries based on that? I guess I understand because it's a weird balance between very important and very unethical:
To me, this is the real "hard problem of consciousness", it's so fundamental and important that it's too valuable to do any kind of testing on. Which means that it's incredibly hard to learn anything about, which means that we're undoubtedly missing out on important information about how consciousness works and how to protect or extend it.