> using the git test suite

That's not actually the case at hand here - the agents were given the original source to reference: https://github.com/gitbutlerapp/grit/blob/main/AGENTS.md#sou...

But for the sake of argument: The test suite itself is copyrighted. To the extent the resulting work is a derivative of the test suite it is possibly infringing. For example you might example that the agent would derive variable names, function names, structure sequence and organization of the code from the test suite. It might even copy comments wholesale. Those are copyrightable things. (Which is of course just the first step in analyzing if it is infringement, there would be interesting fair use, de-minimis copying, etc arguments following a conclusion that any of those were copyrighted. A product produced this way definitely could be infringing given the right facts though).

A GPL tool that processes data doesn't virally transfer the license to its output. Copyrighted ffmpeg code isn't incorporated into the video output. The LLM didn't just conjure up equivalent behavior to git without ingesting the code and transforming it as new output. There is no other behavioral description that would reproduce all needed functionality.

Medium, substitutibility, basics of copyright law.