Mutation Testing in Python with Cosmic Ray
summary
Mutation testing tool Cosmic Ray mutates Python ASTs (via Parso), runs the real test command (usually pytest) and records results in SQLite; a demo runs 67 mutants and later reports 2 survivors. It finds real issues (an unnecessary zero-check in an IBM‑float conversion), supports operator plugins, timeouts/baseline timing to avoid infinite loops, and parallel distributors (local or HTTP). Operators enumerate mutation sites, apply one change at a time, and results are replayable and resumable.
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chapters (11)
- 0:00Introduction
- 1:06Mutation testing theory
- 9:07Code mutation types
- 13:20Practical challenges
- 21:43Cosmic Ray intro
- 28:50Cosmic Ray implementation
- 39:03Cosmic Ray improvements
- 41:10Cosmic Ray demo
- 46:45Results analysis
- 51:01Real-world benefits
- 51:42Q&A
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