muttest-rs

Spec sheet

Purpose

muttest-rs is a Rust mutation testing tool for evaluating whether a test suite catches simulated bugs.Read 9 Oct 2026 · github.com

Intended users

The documented setup is for Rust crate developers who want to assess how well their tests detect code changes.Read 9 Oct 2026 · github.com

License

The repository includes an MIT license that permits use, copying, modification, distribution, sublicensing, and sale subject to its terms.Read 9 Oct 2026 · github.com

Annotation limit

Only top-level items in modules can be annotated with `#[mutate]`.Read 4 Oct 2026 · github.com

Annotation limits

For technical reasons, only top-level items in modules can be annotated with `#[mutate]`.Read 9 Oct 2026 · github.com

Debugging

Setting `RUST_LOG=debug` displays the commands executed during mutation analysis.Read 4 Oct 2026 · github.com

How it works

Its `#[mutate]` macro transforms source code patterns and adds hooks so mutations can be enabled at runtime after a single compilation.Read 9 Oct 2026 · github.com

Installation

The README instructs users to install the `cargo-muttest` Cargo plugin and add `muttest` to their crate.Read 9 Oct 2026 · github.com

Integration tests

The README says integration test analysis uses `muttest` as an optional dependency and runs `cargo muttest` without `--lib`.Read 9 Oct 2026 · github.com

Mutatable code

The tool can mutate runtime-executed expressions, but not const or static definitions, const functions, macros and their arguments, patterns, or types.Read 4 Oct 2026 · github.com

Mutation limits

It cannot mutate const or static definitions, `const fn`s, macros or their arguments, patterns, or types.Read 9 Oct 2026 · github.com

Performance

The README documents an optional `muttest` profile with optimization level 3 and LTO to optimize the test suite during mutation analysis.Read 9 Oct 2026 · github.com

Performance option

The README describes an optional Cargo `muttest` profile with optimization level 3 and link-time optimization for mutation analysis dominated by mutant evaluation.Read 4 Oct 2026 · github.com

Release-code guidance

The README instructs users to ensure muttest does not affect release code.Read 4 Oct 2026 · github.com

Reports

The tool writes a JSON report to `target/muttest/report.json`.Read 9 Oct 2026 · github.com

Runtime mutation

The `#[mutate]` macro transforms selected source patterns and inserts hooks to enable mutations at runtime, allowing the code to be compiled once.Read 4 Oct 2026 · github.com

Test setup

For library tests, the README shows annotating code and test modules, then running `cargo muttest --lib`.Read 9 Oct 2026 · github.com

Unit test workflow

For library mutation analysis, the README directs users to annotate code and test modules, run `cargo muttest --lib`, and inspect `target/muttest/report.json`.Read 4 Oct 2026 · github.com

Where Specifiction places it

• Mutation Testing Tools#25 of 256.5