Interesting.

I ran every kind of virus test I could find about a month ago since I was getting weird display/jank issues. Couldn't find anything, and in the end I tracked the issues down to a windows display scaling error.

Any idea how I would go about testing for a botnet?

I've seen resetting Chrome fix all sorts of weirdness:

https://support.google.com/chrome/answer/3296214?hl=en

Resetting chrome isn't much of a solution if the underlying problem is botnet affiliation (trojan, rootkit, etc). Should be reasonably easy to shut down all applications and services, and inspect the traffic going through the router for suspicious domains. If you only have a windows machine connected there should only be Microsoft traffic and maybe the router manufacturer. Anything else, and it's probably malicious.

Inspecting your PC's traffic from a sniffer on your PC to find a rootkit seems like a fool's errand.

If something has driver / kernel level privileges it can trivially hide such traffic from any sniffer you have running.

Yes, that's why I said to inspect the router's traffic