I'm going to an aspergers assessment. What is it like?

Enjoy it. Since there's no pill or magic cure, the outcome's really moot. Everybody can benefit from some social skills training. Maybe you should choose a sport that's about strength / endurance rather than coordination / teamwork. Aspies enjoy tremendous advantages especially if they focus on science / tech, and if the single life's right for you, that's great. Be nice to others and embrace who you are.
Testing. The psychologist will most likely perform a battery of tests, including: a detailed history, tests of iq and achievement, sensory tests, specific autism questionnaires (others in your ice may be asked to help with these as well), information processing tests, social interaction evaluations, etc.