what is the best way to test a usb power adapter or a micro usb cable? cause in the past i have had problems where the usb power adapter would say a phone is charging but it really wasn't and once i changed it it was all good, also vice versa with the cable, i know this is a good example to know which one has the problem but i would like to know instantly and not a couple days later is there any way?
You left out one other component - the battery, although in truth I've never had to replace one of those on a phone.
In my experience it's rarely the USB cable either, more likely to be a duff charger or not using the right one for that phone.
How to tell which one straight away? - well you can try the same cable on a different, known working device and if that don't work either, bad cable.