A 3 question civics test before you can vote would destroy whole blocs of voters in Australia. Just get them to identify how a progressive income tax works, which country is the biggest greenhouse gas emitter in the OECD, and which parts of the Miranda Rights apply to them, boom PHON gets a dozen votes across the whole country.
Having some kind of extremely-low barrier, pre-declared multiple-choice test questions in order to gain ballot access is an idea I've played around with. Literally mail out a pamphlet with the questions and answers, drafted by the AEC and approved by as many candidates/parties as possible to prevent it being unneutral or propagandised. Objective things like "Which of these services does the federal government handle?" and "Which of these is the typical income of an average Australian?". And if, for whatever reason, you can't answer these simple questions, you aren't informed enough to help decide who represents us in our democratic system.
Relevant, but not quite the same: https://en.wikipedia.org/wiki/Epistemic_democracy