Test network adapter or do-it-yourself network adapter?

Question

Arduino

I would like to find a small compact network adapter for testing the Internet cable. Roughly speaking, two ports, one to enter the Internet, and the other to go to the PC. In general, compact and very cheap to immediately diagnose, the adapter is broken or the provider has problems)
Or if it’s real, then do it yourself using arduino boards, etc.
What can you suggest?

Answer 1

any cheap router
cable tester
you formulate the question so that it becomes clear what you are looking for)

Answer 2

Junior Mikrotik models powered by 5V via usb - can be powered from a power bank / PC