Normally, you can look at a capacitor and tell it’s bad. It will be swollen, particularly at the cap. You can buy a tester for them or use a meter, but to be honest, I think I’ve only seen one or two in my life that weren’t swollen noticeably when they were bad. If the compressor is humming, but not running, look at the capacitor for it. If either fan is trying to turn and won’t, but will spin after you give it a little help, look at the capacitor. When you change one, take a picture of how the wires are on there. Use a pair of insulated needle nose pliers to remove them. Take a screwdriver and put it between the contacts and touch them at the same time. I always did that a couple of times for piece of mind. Once that’s done, swap it out with a capacitor that is either the same or really close. I’ve never tested one to get a reading. Maybe it’s a thing but it seems like a waste of time. Go ahead and grab one or two spares to have one hand for when it does go out.