How do you test if player has tag?

Pls help me anyone. I have literally browsed through the entirety of this forum just to get an answer, but still nothing. I also watched thousands of youtube videos and asked on reddit for help but still no answer. The only thing i ask for is how to check if the player has a tag that was given to it by the command "tag @p add test". I am *NOT* talking about NBT-/Entity or item tags. I ask for the tags that are used in minecraft through the "/tag" command. Please help me if you can!

Thanks in advance!