I think there are two ways to look at the question.
The first being in a typical general election scenario. You should definitely not have to pass a test for this.
I've thought for quite some time though, that on a smaller scale, maybe various municipal scale decisions -- there should be some kind of qualifier to show that you have some background understanding on the subject. Vancouver BC recently had a plebiscite (I hope that's the right word) to determine if they should implement a small tax to pay for mass transit upgrades. There was a large amount of misinformation being spread around, and most people were voting based on their hated of taxes rather than the social benefits that could be realized. I still don't think you should have to pass a test, but maybe at least attend an educational information session geared towards expressing the pros /cons of what is being proposed (with importance placed on having credible, official sources of information).
Maybe there's a way that social structures in the world could start implementing a kind of "proof of stake" system such as we have here. No kids in school? You're not able to determine policy for children's education. Never been in a public school, and you're actively intersted in terring them apart? You're not able to be secretary of education. Etc, etc.