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I agree with Zagorath's sentiment, at present it seems getting more users probably on balance outweighs the risk of the odd troll. However, having to answer a simple question as part of signing up doesn't seem to be too bad at the moment (I signed up before so don't know what the experience is). We don't even need to verify emails at this stage to sign up.

Mature communities don't have major trolling problems because users tend to know not to feed the troll. They're just not engaged and as a result lose air pretty quickly. Forums are a good example - anything that isn't on topic or just clearly a troll is quickly shut down, generally not by moderators but by other users, and there is enough nuance to know what is a valid debate (even if super heated or robust).

"Beating a test" also gives some sense of entitlement, and also it does not stop other users from other instances trolling.

With that in mind, what about a question such as "Do you agree:

1. not to feed the trolls
2. to report any offensive behaviour
3. to look out for your fellow members?"

This is not to weed out the trolls but rather to remind users in such a fashion to nurture a "mature" community that self-regulates.