NERVOUS! ADHD diagnosis....

May I please ask, how is ADHD diagnosed? My husband and I have an appointment coming up soon, to get his ADHD evaluated (upon my request). My biggest worry is to say all the negative things regarding my husband (to the Psychologist) in my husband's presence. I feel like I will be putting him down.

I have read the book "The ADHD effect on Marriage" twice already. It seems to me, what ever is in the book is exactly our life! My Dr who referred us on to the Psychologist does not not think my husband has ADHD ( on the basis that my husband has an engineering degree). Is this true? I am really nervous about our appointment, especially if it doesn't turn out to be ADHD. I am not sure what else can explain everything I feel.