system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why don't we have a department that tests police-citizen relations, i.e. undercover cop cops.

Some way to audit the police and check for abuses of power. Perhaps have someone in a high crime area looking suspicious but not actually breaking the law to make sure protocols are being followed, and to prove people aren't being targeted based on race. It's not like it'd be entrapment any more than using a woman to draw in folks soliciting prostitutes, or acting like a drug dealer/buyer to find users/suppliers.

Edit: U.S. citizen here.
gpt
Here in the US we have entire division and departments that investigate cops and their wrong doing. They are called internal affairs and their only job is to determine if other police are corrupt. And they will implant under cover officers into stations that they believe to be corrupt to conduct investigations. 

TLDR: We do that.