{"categories":[{"label":"Python Modules","url":"https://skillfed.io/packages/category/software-development-libraries-python-modules/12"},{"label":"Testing","url":"https://skillfed.io/packages/category/software-development-testing/3"}],"enrichment":{"capability":"Cosmic Ray is a mutation testing tool that modifies your Python source code and runs your test suite against each mutation to measure test effectiveness and code quality.","skillfed_tags":["test-quality","mutation-testing","code-analysis"],"use_cases":["Assess whether your test suite actually validates the code it claims to cover, beyond line coverage metrics.","Identify weak spots in test logic where mutations slip through undetected.","Measure test quality improvements over time as you refine your test suite.","Validate test effectiveness before deploying critical code to production.","Generate mutation scores for quality gates in continuous integration workflows."],"what_it_does":"Cosmic Ray is a mutation testing framework for Python that systematically modifies your source code\u2014changing operators, literals, and control flow\u2014then reruns your test suite to see if the tests catch the mutations. The goal is to measure how well your tests actually validate your code: if a mutation goes undetected, it reveals a gap in test coverage that a passing test count alone would hide.\n\nYou configure Cosmic Ray with your test runner and target modules, then let it generate and test mutations. It reports which mutations survived (your tests missed them) and which were killed (your tests caught them), giving you a mutation score that reflects test quality. The tool integrates with common Python testing frameworks and can be run from the command line or embedded in CI/CD pipelines.","worth_installing":"Yes, if you want to move beyond line coverage and understand whether your tests actually catch bugs. Cosmic Ray is actively maintained, has low install friction, and uses a permissive MIT license. It's a specialized tool\u2014not for every project\u2014but essential for teams that need confidence in test quality. No known security vulnerabilities."},"id":"cosmic-ray","links":{"html":"https://skillfed.io/packages/cosmic-ray","md":"https://skillfed.io/packages/cosmic-ray.md","pypi":"https://pypi.org/project/cosmic-ray/"},"maintenance":{"status":"active"},"meta":{"latest_release":"2026-08-09","license_spdx":null,"license_treatment":"permissive","name":"cosmic-ray","python_support":"supports_current","summary":"Mutation testing"},"popularity":{"monthly_downloads":362484,"position":7231,"tier":"top_15000"},"security":{"n_vulnerabilities":0},"version":"8.7.0"}