Could someone do some kind of hacked video driver (or something similar) to fool screen sharing, or have a fake ID made so that someone else could take the test in their place? Of course, but that's difficult enough to where fundamentally a vast majority of people simply won't do it. I don't think most cheating deterrents have the goal of eliminating 100% of cheating, but rather the 95+% of potential cheaters who would do the easy stuff.
I mean, if you're willing to put in a lot of effort to cheat on a test, at some point it's easier to just study and pass it legitimately.