In the engine area they spool up the engine to full thrust. Initial engine run happens at the flight line.
Is it possible that sometime first engine run is in the engine test area and sometimes not? I remember me that we can see pictures from the plane with smoke behind the engines (from the oil inside the engine) in the engine test area and sometimes not. If the first engine run was before the plane was moved to the engine test area we should never see the big smoke clouds behind the engine. Or I'm wrong?