We hear all about this practice of kings/rulers having food tasters so they'd be save from assassination by poison. Even Hitler and Stalin had some.
What good were they if they only tasted the food before it was served/still warm? Most poisons don't act that fast. Realisticallly they should have at least waited 12-24h before serving their Lord/Dictator/whatever.
I think that these 3 threads do a good job with describing the role of a food tester and the purpose of having a food tester. Hopefully this will help answer your question.
Are there many cases of a 'food taster' actually consuming poison and dying on the spot?