Comment by alganet

Argument by exaggeration:

For car crash tests, we should always use full humans. A test dummy might have a lot of sensors and be constructed to behave like a human in a crash, but you'll never get the full crash details with a doll.

Notice the problem here? This argument does not consider the costs and risks associated with each approach.

For testing, IO is very expensive. It leads to huge CI setups and testsuites that take multiple hours to run. There is no way around this except using some kind of test double.