Non DJ wanting to test CDJs are fully functional

Greetings,

first time poster here, not actually a DJ at all. I run a small hire company and have CDJs and mixers as part of my inventory. It's getting to the point where some of my gear is getting due for a bit of maintenance and I'm realising, without knowing how to use the gear, I don't really know how to test it beyond putting a CD in and hitting play.

I was wondering if someone could kindly give me some kind of a test guide perhaps?

Gear includes CDJ800s, CDJ88mk2s, CDJ1000mk3s and CDJ2000s. My mixers are DJM600 and 800s. It would be an understatement to say I'm impressed with the amount of stuff both the CDJs and mixers can do.