I cringed so hard when they were testing a jet engine by holding it. That's just asking for trouble.
Rig up a test stand from a bunch of anchored beams and have everyone at a safe distance.
If physical contact is needed stand behind a blast-proof wall and leave only small hole to access the engine, preferably by one of the mass produced golems.
If gasoline isn't available, vegetable oils (obtained by pressing) or ethanol (obtained through distillation) are easily accessible. Or start with a steam engine, since that works with any heat source.
If magic is more convenient just say that instead.
This was so dumb.