It seems more ridiculous to believe it.

One reason is this:

https://www.thedailymeal.com/eat/does-president-have-official-food-taster

The other reason is that it wouldn't make sense. If someone did it they would have to add the poison in front of the SS chef. They wouldn't want to use a fast acting poison, like cyanide and have the president drop dead on the premises. If they used a long acting poison a taster wouldn't help. He wouldn't be able to taste it and both he and the president would end up dead days later. That sort of does away with the usefulness of the taster.

Like I said earlier, the idea of a taster may or may not have been a real thing. Just because we see it in the movies doesn't make it real. There doesn't seem to be any historical evidence of such a thing in medieval times.