The issue with this is that once there is a test to vote, it will become a political tool for disenfranchisement. Questions could be added to systematically suppress votes from particular communities.
Look at the way gerrymandering has been used to isolate populations unfriendly to one party or another.
Any voting test opens the door for the creation of a “ruling class.” And once it is created, then the ruling class will protect its own interests above all else.
There can be no test for voting. All men are created equal, and voting is a right, not a privilege.