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muttest

C
C tier on Mutation Testing ToolsScore 6.6 · #6 of 25
Android app
Not listed
Free plan
No
Runs on
Linux, Mac, Windows
jakubsob.github.io
The muttest homepage
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Summary

muttest is an R package for mutation testing: it makes selected changes to code and runs tests to see which changes the test suite catches. Its mutation score gives the percentage of mutations caught, helping identify weak assertions. Users can choose which changes to apply and where, with mutators for operators, boolean and NA or NULL values, function calls, strings, numbers, indexes, conditions, negation, and return values. Presets group common changes such as arithmetic, comparison, logical, numeric, string, and condition mutations. The package’s examples use testthat and show comparison changes for exposing untested boundary cases. Reports are available in HTML and JSON, with feedback on files that may need stronger assertions. Documentation links a guide for running checks in CI, including GitHub Actions, score badges, and thresholds. A July 2026 update describes parallel execution. muttest is free, licensed under MIT plus a LICENSE file, and supports Linux, macOS, and Windows. The CRAN listing states that it requires R version 4.1.0 or later.

Who it is for

muttest suits R developers who want to check whether their tests catch representative code changes. It may also help review suites generated with LLMs, a use case described by the project.

What is good

  • Reports a percentage mutation score.
  • Offers HTML and JSON reports.
  • Can run in CI with score badges and thresholds.
  • Supports parallel execution.

What to know first

  • Requires R version 4.1.0 or later.
  • The documented test framework includes testthat.

Verdict

muttest helps assess the strength of an R test suite by showing which code mutations pass undetected. Its configurable mutators, reports, and CI guidance give developers several ways to use the results.

Compared on mutation testing tools

Free plan
Yesjakubsob.github.io
Supported languages
Rjakubsob.github.io
Test frameworks
testthat; cucumberjakubsob.github.io
Incremental analysis
Yesjakubsob.github.io
Surviving mutant reports
Yesjakubsob.github.io
Mutation quality gate
Yesjakubsob.github.io
Mutation operators
Binary operators; arithmetic operators; comparison operators; logical operators; boolean literals; NA/NULL literals; numeric literals; string literals; condition negation; function-call names; index increments/decrements; explicit return valuesjakubsob.github.io

Facts

Purpose
muttest mutates R code and runs tests to measure how often the tests catch those changes.jakubsob.r-universe.dev · 3 Oct 2026
Mutation score
The package reports a percentage score for how often tests catch mutations.jakubsob.r-universe.dev · 3 Oct 2026
Configurable mutations
Users choose what code changes to make and where to make them.jakubsob.github.io · 3 Oct 2026
R test workflow
The maker describes muttest as mutation testing for R and shows tests under the testthat framework.jakubsobolewski.com · 3 Oct 2026
Mutation examples
The maker’s examples include changing comparison operators to expose untested boundary cases.jakubsobolewski.com · 3 Oct 2026
Reporting
The package includes HTML and JSON reporting.jakubsobolewski.com · 3 Oct 2026
Parallel execution
The maker’s July 2026 update describes parallel execution as a muttest capability.jakubsobolewski.com · 3 Oct 2026
CI
The documentation index links a guide to running muttest in CI, including GitHub Actions and score badges.jakubsob.r-universe.dev · 3 Oct 2026
Install
The package page provides an R install.packages command using the maker’s r-universe repository and CRAN.jakubsob.r-universe.dev · 3 Oct 2026
Supported build platforms
The package page lists successful checks for Linux, macOS, Windows, and WebAssembly targets.jakubsob.r-universe.dev · 3 Oct 2026
Requirements
The documentation index lists testthat among muttest’s dependencies.jakubsob.r-universe.dev · 3 Oct 2026
Maker
The maker identifies himself as Jakub Sobolewski, a software engineer specializing in R and Shiny.jakubsobolewski.com · 3 Oct 2026
File feedback
The tool reports which files need stronger assertions.github.com · 4 Oct 2026
Mutators
Available mutators include operator, boolean, NA or NULL, function-call, string, numeric, index, condition, negation, and return-value changes.github.com · 4 Oct 2026
Preset mutators
Preset collections cover arithmetic, comparison, logical, boolean, NA, numeric, index, string, and condition mutations.github.com · 4 Oct 2026
HTML report
The package documentation lists a CI vignette describing how to run mutation tests on every push, add a score badge, and enforce thresholds.github.com · 4 Oct 2026
Intended users
The project describes mutation testing as a way to find weak assertions in test suites, including suites generated with LLMs.github.com · 4 Oct 2026
Package type
muttest is an R package for mutation testing.github.com · 4 Oct 2026
License
The package is licensed under MIT plus a LICENSE file.mirror.clarkson.edu · 4 Oct 2026
Runtime requirement
The CRAN package listing states that muttest depends on R version 4.1.0 or later.stat.ethz.ch · 4 Oct 2026
Maintainer
The CRAN package listing names Jakub Sobolewski as author and maintainer.stat.ethz.ch · 4 Oct 2026
Release
The CRAN listing shows version 0.3.0, published July 21, 2026.stat.ethz.ch · 4 Oct 2026

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