Everyone takes tests differently. Depending on your history of taking high-stakes tests -- only you can determine if a real CAT diagnostic test will give you an adequate feel, to go in, and take the real thing.

While it should give you a general idea of the test, the 'real' thing will be different because it's real.

Once you DO take a diagnostic, which I recommend before you begin study, you'll have a sense of how long you need to study. You might not need a few months, but only a few weeks or a month - - depends on what other obligations you have and how efficient you set up your study.

All that said, most people take the test more than once, however, it's most advisable to do this after you study rather than going in cold. Why? Because once you've moved through it as the 'you-who-takes-tests,' you'll have a better idea of what you need to do to close the deal and get your optimal score.

Good Luck.