1-way communication device are used in cheating all the time, it involves of someone that's really good at exams taking the same test, sneak out to the toilet and tell them the answers.
My licensing exam was computer adaptive. We were wanded, turned pockets inside out, videoed. You couldn't eat, take jackets on our off or anything. Lots of rules around how you sat at the table. These must be a fair bit lower tech for the cheating to work. You could wear earplugs and earmuf style sound suppression which I did. Wouldn't be super difficult to have audio in -> but I don't think it would have done much good.
It was done regularly in my highschool in the 2000s, there'd be two or three versions of the test and they'd be distributed randomly. We'd know which one we got because of a label in the corner, which was also how they used the right key for grading.
It'd surprise me if such a simple mitigation wasn't done for more important exams...
Medical licensing exams in the US are randomized within the same sitting, even having two examiners in the same room receiving entirely different questions (not just random question ordering).
I've had plenty of professional and academic exams with multiple different versions of the exam with the questions scrambled. I think almost all of my Bachelor level science courses were provided in that way, as well as multiple Bar exams.
Bluetooth range on headsets is pretty mediocre though. Especially when blocked by body parts. I've never done an exam where the toilets were within Bluetooth range.