Not really sure which forum seemed more appropriate for this but since it covers health/fitness, I reckon it should be okay here.
A number of people wonder whether they have a rotator cuff problem (or other shoulder related problem) and this vid shows how a person can assess if they have a weakness in the rotator cuff area, so I thought you might like to see it, it may come in useful at some point. Ideally you need the assistance of a friend but that shouldn't present a problem.