Just to reiterate what John said.
You are kind of taking the fun out of the restoration, if you test the valves first you do so you might feel that they are little on the low side maybe and go and buy a new valve which means you miss the effect a low valve might have. Also most valves that test low from a TV will in fact work perfectly.
I speak from experience as this is what I wanted to do with my first set, in fact when the set was on it told me what needed doing with a nice purple glow from the EHT rectifier and the output valve
It won't damage anything.
Steve