You know what you're capable of that you don't have to justify. It's possible someone is trying to encourage a response and you're refusing to take the bait. It appears their reason for trying to get you to prove yourself stems mainly from them feeling inadequate. That means it's unnecessary for you to go to lengths you're being encouraged to go to in order to placate an insecure individual. Rise about this. You'll reveal how great you are when it suits you and not before. What are the circumstances that helps or hinders your employment? Find out now!