CONTRIBUTING.rst

Contributing to Mutmut

Setup

First fork the repository and clone your fork.

We use [uv](https://docs.astral.sh/uv/) to manage dependencies. All uv commands will implicitly install the required dependencies, however you can also explicitly install them with uv sync:

uv sync

Running the tests

uv run pytest

We use inline-snapshot for E2E and integration tests, to prevent unexpected changes in the output. If the output _should_ change, you can use uv run pytest --inline-snapshot=fix to update the snapshots.

If pytest terminates before reporting the test failures, it likely hit a case where mutmut calls os._exit(...). Try looking at these calls first for troubleshooting.

Running the tests in a container

Tests are run in CI using a Linux container, if you are not running natively on Linux, you can run the tests in a container using the following script:

./scripts/run_tests.sh

Running your local version of Mutmut against a test codebase

You can install your local version of Mutmut and run it, including any changes you have made, as normal.

Codebases using pip

python -m pip install --editable <path_to_mutmut_codebase>

Codebases using Poetry

poetry add --group dev --editable <path_to_mutmut_codebase>
# Install dependencies in your Poetry environment
pip install -r <path_to_mutmut_codebase>/requirements.txt

Linting and Formatting

This project primarily uses ruff for linting and formatting through pre-commit. You can run the linting and formatting locally with uv run pre-commit run --all-files.

Additionally (and recommended), you can run pre-commit install to install the pre-commit hooks to run automatically when running git commit.

Documentation about mutmut's architecture

Please see ARCHITECTURE.rst for more details on how mutmut works.