The idea of programming as a gear is still controversial, but the specific hypothesized gear is that people who can build a consistent model of a language will be successful at programming, whereas those who can't won't be. This was tested by giving students a test on Java before they had been taught java; their answers were checked, not for correctness, but for consistency. See "The Camel Has Two Humps." Even then the test is far from perfectly predictive- ~28% of the consistent group failed, ~19% of the inconsistent group passed, and membership in the groups as indicated by the tests assigned shifted over time. If you do want to test this, you can reuse the original test.
However, there have been numerous attempted replications, none of which succeeded- though none found a negative result either. They were generally either confounded by the presence of experienced programmers, setup poorly, or not statistically significant. To quote the original authors:
When we began this work we had high hopes that we had found a test that could be used as an admissions filter to reduce the regrettable waste of human e ffort and enthusiasm caused by high failure rates in universities' first programming courses. We can see from the experiments reported above that our test doesn't work if the intake is already experienced, and in experiment 3 didn't work at all. We cannot claim to be separating the programming goats from the non-programming sheep: experiment 3 demolishes the notion that consistent subjects will for the most part learn well, and others for the most part won't. And even in the most encouraging of our results, we find a 50% success rate in those who don't score C0 or CM2 [ie those who were inconsistent]. None the less, some of our results indicate that there may be something going on with consistency.
HT Gwern
It irritates me to no end that the original study is so much better known than the utter failure to replicate. I have to suspect that this has something to do with how conveniently it fits many programmers' notion that programmers are a special sort of person, possessed of some power beyond merely a lot of practice at programming and related skills.
People on this board have talked about programming as a gear in your brain that, to a first approximation, you have or you don't. I'm wondering if there's some well put-together resource you can direct someone with zero experience and just a web-browser to and say "if you're having fun an hour from now, you have the gear, good luck" -- maybe something on Khan academy?
(I learned to program a long time ago, and I started with BASIC program listings in my math textbook -- I don't actually know what the optimal onramps are now.)