An engine in a test bed does NOTHING except churn up air thereby producing heat. If the object an engine is attached to does not increase in the total of GPE +KE as a result of the efforts of the engine then no *useful* work is being done. Likewise a person straining on a wrench is just producing heat. In both cases energy is certainly used, but not usefully.
Had the dirt track car on the dyno yesterday. Watched very carefully and am sure the car did not move an inch.
Yet the dyno showed 327 rear wheel horsepower at 7200 RPM.
Lots of heat and noise, used 27 litres of fuel.