Dead Probes Pass: Mutation-Check Your Characterization Tests Before You Refactor

Description and use

Verify that your tests actually detect bugs by performing a mutation audit: create three mutations per behavior, run the probe‑versus‑mutation matrix, and keep only alive tests that fail on at least one mutation.

Problem

Legacy code has passing tests that give false confidence because the tests do not detect bugs; refactoring risks introducing regressions.

Outcome

After a 20‑minute audit, dead probes are identified and removed, leaving a minimal set of alive probes that detect mutations, providing a safety net for refactoring.

Workflow

• Draft probes with a free LLM model
• Draft three mutations per behavior
• Run probe‑versus‑mutation matrix on a free server
• Keep only probes that catch at least one mutation

Evidence

A probe earns trust by failing on mutated code.

Source

Four steps. No paid tools. No local GPU.

Source