Servos and batteries/switches are weak points in our control systems.

In electronics you have the bathtub curve of failures. A short burn-in period is often used to catch infant mortality. For a servo, the electronics might be well served by operating them for 24-48 hours, but the motors and pots would not helped by such a lengthy test period if moving over that time period.

A few minutes of operation, listening to the servo and slightly loading it as suggested by Andy in post 2 will tell you all you need to know.

However for the truly paranoid, you can cool the radio to freezing and test it's function, then heat the radio to about 130 degrees and test. The expansion and contraction of PC boards and solder joints will uncover problems that may exist. Also test against vibration by placing it on a jig saw and buzz at different speeds.

Then, before the first flight of the day, range check and check batteries before each flight under a fixed load.

For bigger airplanes, use dual elevator and dual aileron servos. This will save the bacon 90% of the time.

Most crashes are pilot error, so ...