CASA individuals FOIs make it clear to instructor that "engine failure" means engine failure, none of this whimpy zero thrust nonsense.
Just to wrap up discussing my method, once the failed engine had been identified, verified and the student touched the appropriate pitch lever (calling feather left/right), zero thrust would be set. This involved at MP and RPM setting with the mixture set back to rich. From memory about 10" MP, 2200 RPM or something like that.
Avgas and others, I guess we'll agree to disagree that the engine was shut down. As mentioned previously, power was immediately available once the mixture was restored. This method was different to that of some pilots who used fuel shut offs etc to kill the engine. That is an entirely different kettle of fish that I don't support as a delay could be expected restoring power using such an approach.