Many thanks guys for the quality and helpfulness of your replies. It does appear that a significant majority of us are in favour of, or at least have nothing against, engineers/mechanics performing helicopter engine ground-runs - but with proper training and strict limits on what can and cannot be done - no objection there.
To Troglodita (#20) and Helinut (#26) I would say that your referred definitions are for 'flight time' which is used by pilots, i.e. flight and duty time limitations. Also, remember that apart from post engine wash drying runs, the helicopter is probably unserviceable (if an engineer/mechanic is running it) and therefore the question of 'flight' is not applicable. However, if you meant the amount of engine operating time for maintenance tracking purposes then this is calculated by using 'time-in-service' and is not applicable to ground operations.
EN48 (#17), nice one......