This seems like a near perfect use of coding LLMs and a useful way to implement reinforcement learning.

“Add a major bug to this file that is not covered by existing tests” vs “Find the bug in this file” vs “write a sensible test in this file that protects against this type of bug”

This is called mutation testing and is very common in formal silicon verification.

https://en.wikipedia.org/wiki/Mutation_testing

A downside of naively changing source code is that you have to recompile the code for every mutant, which can be very slow (especially for Rust!). Obviously the right thing to do is to decide at runtime whether to insert a bug or not for each mutation point.

I had a brief skim through the help for cargo-mutants and it looks like it takes the naive approach which is rather unfortunate.

Here's a list of mutation testing tools for various languages: https://github.com/theofidry/awesome-mutation-testing

If you're looking for an option for Go, https://github.com/gtramontina/ooze can be of help. It was heavily inspired by https://github.com/zimmski/go-mutesting

At RustConf 2024 in Montreal, Cargo-mutants' creator Martin Pool's presentation was excellent. One of the best sessions of the conference.

https://www.youtube.com/watch?v=PjDHe-PkOy8

Really cool! I wish there was such a thing for JavaScript.

I say this as a so-so software engineer. I badly wish there was more emphasis on increasing software quality. There is so much the industry could do to radically improve quality, such as tools like this.

I know the incentives just aren't there, but still.