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mutator

mutator is a free mutation testing tool for the R language.

Place
#20 of 25
Score
5.3
mutator's website

What mutator is

mutator is a free mutation testing tool for the R language. It changes source code through abstract syntax tree mutations, then checks whether a package’s tests detect those changes. The reported mutation score is the ratio of killed mutants to all mutants, giving developers a measure of test-suite effectiveness. Mutation operators cover arithmetic, comparisons, logic, constants, return values, and statement deletion. mutator supports testthat and tinytest, plus a generic installed-tests fallback. Parallel execution is available. Coverage-guided selection runs tests covering each mutated line for testthat and tinytest; the generic fallback warns and runs the full suite. Per-mutant timeouts are calibrated to identify hangs, with user overrides available, and users can cap mutant counts. A reusable GitHub Actions workflow supports continuous integration. Surviving-mutant reports and a mutation quality gate are included. Likely equivalent mutants can be flagged through an OpenAI-compatible API. The GPL (>= 3) package is installable from CRAN, with development versions on GitHub and R-universe.

Good

  • Measures test effectiveness with a mutation score
  • Supports testthat and tinytest frameworks
  • Runs tests in parallel
  • Provides coverage-guided test selection
  • Includes GitHub Actions integration

Watch out

  • Generic fallback runs the full test suite
  • Coverage guidance is unavailable for generic fallback
  • Equivalent-mutant detection needs an OpenAI-compatible API

Who it suits

mutator is for R developers assessing and improving package test suites. It suits projects using testthat, tinytest, or installed-test layouts.

Verdict

mutator provides configurable mutation testing for R packages, including reports, quality gates, and CI support. Its testing strategy affects whether coverage-guided selection is available.

The facts

Each one read from mutator's own pages, with the date it was checked.

What it does

AST mutations
mutator applies mutations at the abstract syntax tree level.checked 7 Oct 2026
CI integration
It provides a reusable GitHub Actions workflow for mutation testing, including optional mutation-score thresholds and badge publishing.checked 7 Oct 2026
Developers
The project is developed by Pierre Donat-Bouillud and Assanali Amandykov.checked 7 Oct 2026
Equivalent mutants
It can use LLMs to flag likely equivalent mutants through a configurable OpenAI-compatible API.checked 7 Oct 2026
Execution speed
It supports parallel test execution and coverage-guided selection that runs only tests covering each mutated line.checked 7 Oct 2026
Installation
The released version can be installed from CRAN with install.packages("mutator"), and development versions are available from GitHub and R-universe.checked 7 Oct 2026
Intended users
The tool is for developers seeking to assess and improve R package test suites.checked 7 Oct 2026
License
The package is licensed under GPL (>= 3).checked 7 Oct 2026
Limits and configuration
Users can cap the number of mutants and set a per-mutant timeout; coverage-guided selection falls back to the full suite for the generic installed-tests strategy.checked 7 Oct 2026
LLM integration
Equivalent-mutant detection can use an OpenAI-compatible API.checked 7 Oct 2026
Mutation method
It uses abstract syntax tree analysis and mutation operators for arithmetic, comparisons, logic, constants, return values, and statement deletion.checked 7 Oct 2026
Mutation operators
Its operators include arithmetic, comparison and logical changes, constant and return-value replacements, and statement deletions.checked 7 Oct 2026
Mutation score
It reports the ratio of killed mutants to total mutants as a measure of test suite effectiveness.checked 7 Oct 2026
Notable limit
Coverage-guided selection is on by default for testthat and tinytest strategies; with the generic installed-tests fallback, it warns and runs the full suite.checked 7 Oct 2026
Performance
It supports parallel test execution and coverage-guided test selection, which runs tests covering each mutated line.checked 7 Oct 2026
Purpose
mutator is an automated mutation testing tool for the R language that checks whether a test suite detects systematic changes to source code.checked 7 Oct 2026
Support
The documentation links to a GitHub page for reporting bugs.checked 7 Oct 2026
Test harnesses
It supports testthat and tinytest, with a generic installed-tests fallback for other layouts.checked 7 Oct 2026
Timeouts
It self-calibrates per-mutant timeouts to detect hangs, and users can override the timeout.checked 7 Oct 2026

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