Drivers don't require any particular hardware to function -- they can be triggered to autoload on hardware detection, but you can also trigger them on demand, or on startup. As an example, ProcExp uses a driver to list open handles.

If you're interested in running kernel code on your own device, it's simpler to just write your own driver.

You can't run unsigned kernel drivers unless you boot the operating system in test mode, right?

Correct. It's advisable to do it on a VM or another computer you own, rather than your main computer.

Sure, but this is in the context of wanting to run kernel code to cheat in a video game (which is what that forum post is about)

I feel like I'm missing something here. You can run games in test mode. Anticheat code will obviously trip, hence, the hiding... But anticheat also trips if you have the wrong brand of mouse. The context is informative, but doesn't really change anything?

Fortnite for example refuses to run if you boot in test mode. I don't play online much so I assumed it was standard behaviour in multiplayer games.