Mutation Testing: The Deterministic Arbiter of LLM-Generated Tests
This blog documents learnings from building Angzarr—a polyglot event sourcing framework. The framework core is written in Rust, so examples here are primarily Rust.
Angzarr doesn't require Rust. Client SDKs exist for Go, Python, Java, C#, and C++. The author—a polyglot developer—doesn't believe Rust is the best language for everything. It is the right choice for this framework's core, and building it has produced these learnings.
The Rust should be readable by most programmers. If you have questions: consult The Rust Book, ask an LLM, or email the author.
Last week I argued that you should build deterministic systems with non-deterministic tools—demand TDD from your LLM, get tests first, then implementation. But there's a problem with that workflow: passing tests aren't proof that tests are good.
Enter mutation testing: a deterministic tool that validates whether your tests actually test anything.