Actually Claude just did something similar for me, as I'm working on something else with Quake.

On its own it decided to do demo playbacks and take periodic snapshots, and compare them pixel by pixel if the PNGs differ.

I was also working on a web-based port but it saw the original Quake code was not modified so it compiled a native version on its own to use for this.

It had to apply a small patch to make the game completely deterministic, but it figured that out on its own by reading the code.

It then asked me to record a demo with various elements, say an explosion or being under water, and visually verified that the screenshots had those elements present.

So now I have a solid set of tests to verify against.

Opus 5.5 Medium. Used at most 1% of the weekly limit of my $20 plan.