go-mutesting vs Muter

go-mutesting is a framework for mutation testing Go code to identify parts of a program that tests may not cover. It changes source code in controlled ways, runs tests, and reports whether each mutation is killed or survives; surviving mutations are accompanied by a source patch. Its mutation score reflects the share of generated mutations killed by the test suite. Targets may be Go files, directories, or packages, including recursive `...` patterns, while `_test` files are excluded. By default, it replaces the original file with a mutation and runs that package’s tests. Alternatively, an external command can test each mutation, with environment variables describing the change and exit codes indicating the result. Built-in mutators cover branches, comparisons, boolean expressions, statement removal, and Cosmos SDK arithmetic and comparisons. Custom mutators can be registered through the Mutator interface. The MIT-licensed tool is free and runs on Linux or in self-hosted environments. Its README positions mutation testing as a supplement to automatic test suites and cautions that false positives can occur.

Muter is a free, open-source mutation testing utility for Swift test suites on macOS. It changes code in a complete copy of the codebase, leaving the original untouched, then reports mutation scores for the full suite and individual files. Runs can happen in Xcode, from the command line or incrementally in continuous integration. Configuration covers Xcode projects, workspaces and Swift Package Manager. Reports can be plain text, JSON, HTML or Xcode issue navigator results, including surviving mutants. Documented operators replace relational operators, remove side effects, change logical connectors and swap ternary expressions. Muter supports projects tested with xcodebuild, including iOS, macOS, tvOS and watchOS applications, but the utility runs only on macOS 10.15 or newer. It supports Swift, not Objective-C. Any test target or suite can be used with Swift application code, although UI tests may take a long time. The project states that it has no network access and collects no analytics.