Captplaystation.
There is no case for having a pilot on the flight deck when doing an engine run above idle power. I would even go as far to say that the engineers are better trained to deal with these situations then the pilots are. (Ducks for cover from flying flight cases!). How often do we as pilots perform an engine run at max power for several minutes with the brakes on?
Normally when we (pilots) perform a max thrust take-off we are staring down a nice 'long' runway. If something goes wrong (i.e. Brake failure) then we got a reasonable time period to react.
If the engineers perform a max thrust engine run then this is often done in the engine test bay which is sometimes open at the front or, as at some noise sensitive airports, is completely enclosed. Hence, the time to react is a lot shorter.
Before I started flying I worked as an engineer and performed engine runs on a near daily basis, from idle runs to the less frequent high power runs. Every year we had a sim session to train for emergencies and the aircraft jumping its chocks etc was part of this. However I am not sure if this was a regulatory requirement or just a company requirement.
Procedures and checklists are in place to mitigate against any problems. But very similar to pilots, the engineers also face time pressure. Especially when an aircraft is taken out of service in the middle of a series of flights. Not saying at all that this contributed to this accident but as with anything there is a chance that corners get cut when under time pressure.