Testing isn't easy or cheap. I have a tube tester, Hickok 534B. Just checked and I don't have test data (anyway at first glace) for KT120.
I like to test tubes before using them but the important test is for shorts. this can be done with a multimeter. Check each pin isn't shorted to another pin. If you do find 2 pins shorted, pull the tube data sheet as they may be connected internally. If they aren't supposed to be shorted, don't use them.
The actual tube test data isn't as important but very nice to know.
Maybe someone will suggest a differet tester that does have settings for the KT120.
Jerry