That's what the GP proposed.
For a human, a skill test is OK, because we already know he's a human, and cities are built around humans. We can expect him to behave in a certain way, and we kind of know his possible range of abilities and limitations, even if not in a formal way.
There's a reason why we require other things, like a minimum age, because being a responsible adult is precondition to the test.
What they are doing right now is different. Still a black box test, but much more comprehensive. They are going to gather so much data that statistics are going to start kicking in, bc they should be able to somewhat "prove" that these cars are safer than regular cars.