I think that some (most?) airlines require 2 people to be present on the flight deck for engine running.
If you were alone you might well ask for assistance from an aircrew member (if you could find one!!).
The aircrew member would be acting in lieu of the second engineer and prime responsibility would lie with the engineer in charge of the ground run.
There would be no captains acceptance signed in the tech log and the aircraft would be engineerings responsibility.