go-mutesting vs mutmut

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.

mutmut is a free, open-source mutation testing system for Python. It makes small code changes called mutants so developers can check whether tests detect them. Its listed operators increment integer literals by one, change < to <=, and swap break and continue. The project supports pytest and remembers completed work for incremental runs, selecting tests to run for each mutant. An interactive terminal interface lets users browse mutants, write one to disk, and rerun individual cases after adding tests. Runs are described as parallel; configured coverage.py can restrict mutations to covered lines. The documentation also supports filtering with mypy or pyrefly, but not pyright or ty. For CI/CD, mutmut can export statistics and generate mutation-score badge JSON for a Shields endpoint. Configuration in setup.cfg or pyproject.toml can specify source paths and pytest selection arguments. It requires Python 3.10 or later and a system with fork support, so Windows users need WSL. Version 3 and later mutate code inside functions; version 2 uses a different model for code outside functions. The package is licensed under BSD-3-Clause.