Comparison¶
irradiate vs mutmut¶
irradiate is heavily inspired by mutmut and shares its trampoline architecture, naming conventions, and config format. The main differences are in execution model and feature set.
| mutmut 3.5.0 | irradiate | |
|---|---|---|
| Execution | Fork-from-parent (zero startup per mutant) | Fork-per-mutant inside pre-warmed worker pool |
| Test filtering | Coverage-based (since 3.x) | Coverage-based with priority scheduling |
| Parser | LibCST (Python, sequential) | tree-sitter (Rust, parallel via rayon) |
| Operators | 14 categories | 38 categories (27 tree-sitter + 11 regex) |
| Cache | mtime-based (breaks on rebase, touch) | Content-addressable (SHA-256) |
| Orchestration | Python multiprocessing | Rust + tokio async |
| Incremental | -- | --diff with merge-base resolution |
| Reports | Terminal only | JSON (Stryker v2), HTML, GitHub Actions annotations |
| Decorator support | Skip all | All decorators handled (trampoline + source-patch) + decorator_removal operator |
| CI integration | Manual | --fail-under, inline annotations, step summary |
| Isolation | Fork only | Warm-session + --isolate + --verify-survivors |
| Config | [tool.mutmut] | [tool.irradiate] (mutmut section accepted with deprecation warning) |
mutmut is faster on small projects with fast test suites (< 500 mutants). irradiate is faster on larger projects where its bounded memory and duration-aware scheduling outweigh the startup overhead, and is more reliable on codebases with pre-existing test failures or macOS environments. See Performance for detailed benchmarks.
Python ecosystem¶
cosmic-ray¶
Parso-based. Generates all pairwise operator permutations rather than curated swap tables. Supports non-pytest test runners via its session/worker model. Good choice if you need a custom test runner or want exhaustive operator coverage over speed.
mutpy¶
Python ast-based. Follows academic mutation operator naming (AOR, ROR, etc.). Has object-oriented mutation operators not found elsewhere: inheritance manipulation, self.x to x, slice index removal. Largely unmaintained.
Other ecosystems¶
cargo-mutants (Rust)¶
Closest equivalent in design philosophy. Primary strategy is function body replacement — replace the entire body with a type-appropriate default. Simpler to reason about than fine-grained operator swaps but produces fewer total mutations.
Stryker (JS/TS)¶
The most feature-rich JS/TS mutation tester. JS-specific operators: optional chaining removal, array/object emptying, regex mutation. Runs as a Node.js process.
PIT / pitest (Java)¶
Most widely-used JVM mutation tester. Operates on bytecode, making it language-agnostic across JVM languages. Elaborate operator tier system (DEFAULTS vs STRONGER vs ALL) and a commercial extension (Arcmutate).
Infection (PHP)¶
The most operator-dense framework, with 200+ distinct mutation operators. PHP-specific mutations: function unwrapping (strip a call, return its argument), type cast removal, visibility reduction.