I've seen it as well....
The last station of the engine assembly line, engines are fitted with adapters, filled with oil and then proceed to the next station, the dyno room.
The motor is then hooked up to the Dyno in a sound proof room, and put through the paces for 30 minutes. Porsche refers to this as the "Hot Test".

The following hot test is the final step in the engine production process. The engines are first of all heated up to operating temperature and then subjected to a functional test including full-throttle testing. Information in the form of up to 220 parameters is generated in this test of around five minutes' duration.

The engine must produce at least 100% of it's rated horsepower, or it is unacceptable.

Each and every engine assembled gets dynoed

Each engine is assembled for a particular car by one tech.



That is exactly what I witnessed when I went thru the factory tour