This is one of those things that will keep me reading all the comments. Over the years we have come up with our own system. There is two radios. Ones that work and ones that don't. The third group is the ones that work sometimes and don't at others. The group three is the ones nobody likes.
We have a trainer. This thing could be a test bed for glue. It seems every kind of glue ever made has been used to repair it. The old boy (the beat up trainer) has become a test bed for radios and related equipment. We have found all sorts of things in flying conditions. We are all surprised at how many radio failures was caused by the switch. The list goes on. Checking out a radio in a beat up old trainer is one way to overcome fear. The old trainer don't seem to mind some more glue.