Presumably, he/she wants to apply.
The tests are not the paper and pencil type that NATS prefers, but a very simple (well, they must be simple... I passed them!) computer based thing that lasts 2 hours at the most.
About the only thing that you can do to improve your performance in these tests is make sure your mental arithmetic is up to speed (about 10 minutes a day for 2 weeks preceeding the tests should do, with the focus on accuracy at high speed). And get a good night's sleep beforehand.