Gandalf's power says that, when you discard a card with an icon fate, you can scout 1 and get 1 ispiration.

I wonder: if I a discard a card during a test (for example an attack), can I get the inspiration (and can I scout) DURING the attack and use that inspiration and that card to convert fate in success?

yes, I would say you can if you can discard the card you can capitalize on Gandalf's ability

Yes, I believe that is a legitimate example for Gandalf's personal ability.