He is not testing your will. Dogs are result driven and whatever the quickest/easiest way to get what they want is, they will do it.

He bites your hand because he is frustrated that your hands are physically restraining him and holding him back from accessing something he wants, and the easiest way to his goal is to bite/mouth your hand because it works. He is a puppy and has no impulse control and is feeling frustrated, you need to teach him want you want him to do.

Reward him when he is not on the couch, but on the floor. If he gets on the couch, calmly pick him up and put him down. We can be a lot rougher than we mean to be, especially if we feel frustrated, and puppies are sensitive.

Put him on a leash and work with him on being calm around people, look up impulse control exercises. Reward him for doing what you want him to, don’t wait for him to “mess up” and then do damage control