Not as wide as you think an not used as often as portrayed by media. Royal/Presidential taste testers are still used to this day to diminish the threat of poison. It's an actual job and has a payroll, much akin to being a dare devil or any other risky job which could cause you your life.

Reagan and Bush both were known to use food tasters, usually when it's a cause and they're widely disliked in their country. Notice both of these presidents weren't very popular?

Also any good or noteable poison has instant effects and, before the food is even served the tester would try it out (such as after the kitchen before being served.) not at the table with the President/King as they're about to eat. It would be ingested in advance.

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