This is always shot down because eventually someone in control will change the test to introduce bias in their favor.
But, what if: Make there be one concrete, completely unchangeable rule. The test must be a math question.
No hypothetical story to make the question 'relevant' (E.g. Bob and Alice each have x and y ... calculate z). Just raw math.
There is no biasing a math question.
Perhaps an integral or differential equation with randomly chosen constants.
Yeah, it doesn't filter for civic education.
Yeah, people could prepare and/or give out targeted explainers for the type of question after first voting/mail-in voting day.
Yeah, it will still let some shitty people vote and deny some good people from voting.
But there is no biasing a math question.
Probably will still have more problems in practice. Big ones being making an 'unchangeable' rule, or it being made ineffective by changing the question to something like simple addition.
Not necessarily saying this should be done or is a good idea. Just putting the thought out there.