cosmic-ray

library8.4.6pypypi✓ verified 86d ago

Cosmic Ray is a mutation testing tool for Python. It runs tests against mutated versions of your code to assess test suite quality. Current version 8.4.6. Release cadence is irregular with several minor releases per year.

testing

pip install cosmic-ray

github ↗package ↗homepage ↗

INSTALL

IMPORT

SIG · COSMIC-RAY

cosmic-ray

testingpythonv8.4.6

harness data pending

Install & Compatibility

Where this runs

No compatibility data collected yet for this library.

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

main

✓ from cosmic_ray.cli import main

✗ from cosmic_ray import main

main is in the cli submodule, not top-level

Quickstart: Run cosmic-ray mutation testing on a module using pytest as the test runner.

from cosmic_ray.cli import main import sys # Run mutation test on a specific module sys.argv = ['cosmic-ray', '--baseline=10', 'test', '--tests', 'pytest', '--executor', 'local', 'my_module.py'] main()

cosmic-ray --version

Debug

Known issues

breakingIn version 8.0.0, the CLI command structure changed from `cosmic-ray <subcommand>` to `cosmic-ray <subcommand> ...` with different argument order. Old scripts using positional arguments will break.

fix

Update to new CLI syntax: `cosmic-ray test --tests pytest --executor local my_module.py`

affects: <8.0.0

deprecatedThe `--baseline` option is deprecated in version 8.4.0 and may be removed in future versions. Use `--timeout` instead.

fix

Replace `--baseline` with `--timeout` (value in seconds).

affects: >=8.4.0

gotchaCosmic Ray requires an executor (local, celery, etc.). Default is not set; you must specify `--executor local` or configure one.

fix

Always include `--executor local` for local execution.

affects: all

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'cosmic_ray'

Package name on PyPI is 'cosmic-ray' (with a dash), but the import uses underscore.

fix

Install with pip: `pip install cosmic-ray`. Import with: `import cosmic_ray`.

NameError: name 'main' is not defined

The main entry point is in the cli submodule, not at the package root.

fix

Use `from cosmic_ray.cli import main` instead of `from cosmic_ray import main`.

Upgrade

Version history

8.4.6latest on PyPI · released Apr 2, 2026

Audit

Dependencies

pytestoptionalRequired for running tests with pytest plugin

Agent activity

11 hits · last 30 days

node

OpenAI (training)

Resources

githubhttps://github.com/sixty-north/cosmic-ray ↗

packagehttps://pypi.org/project/cosmic-ray/ ↗

homepagehttps://cosmic-ray.readthedocs.io ↗