In Blade Runner (1982), Deckard used the Voight-Kampff test to detect Replicants. This complicated test verified if their emotional response was appropriate. But they also displayed superhuman capabilities, were shown to take a lot more damage than humans can, and so on.
Why is it so hard to detect them if they have enhanced physical capacity? Wouldn't that enhanced capacity imply some physiological difference? Or why not just test their capacity directly?