Mutate (tool)

type: module path: tools/Mutate.pudu

Purpose and Interface

Mutation testing: apply one operator change at a time to source files, run the checks and the suites, and report survivors.

pudu run tools/Mutate.pudu [--file <path> | --domain] [--every <n>] [--threshold <percent>] [--dry-run], with PUDU_BIN naming the compiler (default pudu).

Algorithm and edge cases

Mutants are operator swaps at code positions outside strings, comments, and imports; comparisons must be spaced so type brackets are not mutated.

A mutant that fails pudu check is invalid; one whose suites still pass survived.

--domain limits the run to the pure predicate layer under src/PuduLangValidator/Rules; --every n samples; --threshold fails the run below a score.

Negative logic

No background mutation without a verdict. Every mutated file is restored before the next mutant, whatever the verdict.

A mutant whose suites run past 60 seconds counts as killed.

The harness runs on a committed tree only: a run stopped mid-mutant leaves that one change, which git diff shows and git checkout removes.

Depth

MEDIUM — one operator change per run with full suite adjudication.

Grill Log

• Q: Why mutate the predicate layer in pull requests? A: It holds the comparisons where a single-point change is most likely to go unnoticed, and it runs in minutes. Rationale: boundary mistakes hide in plain operators. Rejected: the full tree on every pull request.
• Q: What happens to a mutant that cannot change behaviour? A: The code is simplified until the mutant is invalid or killed. Rationale: an unkillable mutant marks a redundant expression. Rejected: excusing survivors.

Referenced by

[[src/_MOC]]