Sort of like the concept of a "lie detector," designed to tell whether or not someone is telling the truth, the Voigt-Kampff Empathy Test is designed to tell androids apart from human based on the fraction of a section it takes an android to feign an empathetic reaction.

This Empathy Test measured your capillary action and some other patch was attached to your cheek to measure face expression. It was a series of questions that regarded on empathy for animals and sometimes for humans. The results heavily depended not on your worded answer but on the psychological effect the question had on you.
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In Chapter 5 however, Rachael, after it was detected that she was an android, the Rosens said that she was not, invalidating the Voight-Kampff empathy test. Rick was now in an uncomfortable position, and to make it worse, Rachael says, "We have you, Mr. Deckard" (55)
"If you can't agree to that, go on back to San Francisco and admit to your superiors in the department that the Voigt-Kampff scale, at least as admistered by you, can't distinguish an andy from a human being. And then look for another job." (58)
Eventually, Rick asks another question to Rachael, and finally concludes that she is, in fact, a humanoid android.

This Voigt-Empathy Test has been used for a very long time against androids and telling apart humans from androids. If there was ever a doubt or a mistake with this test it would lead to dire consequences. If it was wrong it could either
a) Let an android escape because the results resulted as a human
b) Kill a human being because the results said it was an android.
So far, this test seems to be very dependable other than going through a bone marrow test.
A lot of pressure was put on this test and doubt was is its main force

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As you can see here a clip form the movie blade runner, a movie based on this novel, he is seated here with the machine using it.
In the movie this test is used a couple of times to determine weather the thing is human or android.