There is no excuse or reason, for an instructor to be horrible to their students.
Nor should they operate controls when they - the instructor - is supposed to be Pilot Monitoring or Instructor Testing - unless there is an emergency, in which case they should state "I have control".
I flew 2 crew airline operations with an ex Jaguar pilot, (single seat fast jet), and he was a bit like your guy.
After he had fiddled with my settings and selections a few times during one flight, I called him on it. "why are you doing that? I thought I was pilot flying". He immediately apologised and told me to call him out if he ever did it again. It was largely habit from his previous flying.
You don't have to be cross or shout or argue. Just say "I am confused that you are making selections without me asking, because I thought I was the pilot flying". Depending on his answer, you can either carry on, or say "you have control, and I am terminating this check ride".
You are effectively paying their wages, so you don't have to put up with their bad behaviour.