dart_mutant

Mutation testing for Dart. AST-based, parallel, written in Rust.

Code coverage tells you what code runs. Mutation testing tells you what code your tests actually verify. dart_mutant injects small bugs (mutants) into your code and runs dart test to see which ones your tests catch.

Install

macOS (Apple Silicon) and Linux (x64) — Homebrew

brew install nimblesite/tap/dart_mutant

Works on macOS (Apple Silicon) and any Linux distro with Homebrew on Linux installed.

Windows (x64) — Scoop

scoop bucket add nimblesite https://github.com/Nimblesite/scoop-bucket
scoop install dart_mutant

Other platforms — from source

Requires Rust 1.75+:

git clone https://github.com/Nimblesite/dart_mutant
cd dart_mutant
cargo build --release
export PATH="$PATH:$(pwd)/target/release"

Usage

cd your_dart_project
dart_mutant

Open ./mutation-reports/mutation-report.html to see what your tests missed.

Common options

dart_mutant -j 8                          # parallel jobs (default: CPU count)
dart_mutant --sample 50                   # quick feedback on a subset
dart_mutant --threshold 80                # fail if score < 80
dart_mutant --incremental --base-ref main # only test changed files

Full reference: dart_mutant --help.

Reports

Flag	Output	Use case
--html (default)	Interactive HTML dashboard	Human review
--json	Stryker-compatible JSON	CI dashboards
--junit	JUnit XML	CI test results
--ai-report	LLM-optimized markdown	Paste into Claude/ChatGPT

The AI report groups surviving mutants by file with line numbers and test hints, ready for an LLM to write the missing tests.

Mutation operators

Category	Examples
Arithmetic	+ ↔ -, * ↔ /, ++ ↔ --
Comparison	> ↔ >=, < ↔ <=, == ↔ !=
Logical	&& ↔ ||, ! removal
Null safety	?? removal, ?. → .
Control flow	if(x) → if(true) / if(false)
Literals	true ↔ false, "str" → ""

See docs/operators for the full list.

Results

• Killed — a test failed when the mutation was applied (good)
• Survived — every test still passed (a gap in your suite)
• Timeout — the mutation caused the test to hang (counted as killed)

License

MIT. Copyright (c) 2026 Nimblesite. See LICENSE.

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Maintained by Nimblesite. Docs at dartmutant.dev.