I’ve had this conversation before. And you are right. If done improperly you could inadvertently end up with a ruling class by way of the enfranchised continually voting to make their group ever more exclusive.
To this I respond that we already *do* have a voting test. The test is “Are you older than 18 and not a felon?” It already *is* politicized. Winston Churchill observed that “If You Are Not a Liberal at 25, You Have No Heart. If You Are Not a Conservative at 35 You Have No Brain”. In other words younger people lean left and older people lean right. Consequently when a liberal party has enough clout it might attempt to lower the voting age to entrench itself.
Conversely many conservative minded people have the exact same idea in the opposite direction.
The felon part of the test isn’t that great either since a party with sufficient clout can turn minor crimes into felonies for the purpose of disenfranchisement.
Yet the voting age doesn’t fluctuate constantly. Neither party has ever gotten to the critical mass of power where they can pass constitutional amendments to entrench their own power.
All I’m saying is the current test (18, not felon) is a very poor test. It has a ton of false positives (people who really shouldn’t vote) and more than a few false negatives (young engaged people who can’t vote). Let’s replace it with something smarter.
For example: every candidate on the ballot gets to pick 5 multiple choice questions. The ballots of people who score in the bottom 20% are thrown out. This ensures that the questions are equally partisan, that a large majority is always enfranchised, and only people who cared enough to do basic research into the issues are counted.
Note: There are some restrictions on the type of questions which I am not mentioning here. Short version is the questions need to somehow relate to something the president can do. E.g a candidate cannot take advantage of their core demographic by asking a sports question on the ballot.