Maybe taster is just for food? and tester is just for things? Or what's the difference?
A taster is not just for food.
For example, if a school is offering a course of classes in a subject, you may be able to take - as a one-off - one lesson that's either free or cut-price. You can take this, without any obligation, to find out whether the course is for you or not. This is a 'taster' because it gives you a 'taste' of what the whole course will be like.
'Tester' tends to be used for products such as cosmetics and perfumes.
I knew that "tester" is a kind of electrical instrument to know the flow of current in a wire. By the way, nice to know about different usages of tester and taster. Thank you:)
Here is a tester