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implemented（除 4 篇超长文档随后补）、proposed、rejected 全树配对； 同一流水线 + 二遍校验（paraphrase-back + 仓库上下文一致性）产出。 docs/rfc/implemented/AGENTS.md 与其 CLAUDE.md 符号链接列入排除 （agent 指令文件，与根 AGENTS.md 同策略）。
2.1 KiB
2.1 KiB
RFC: Mutation testing as the coverage counterweight
English | 中文
Status: proposed
Problem
The per-file 100% coverage gate (the quality-gates decision) proves every line executes under test — not that any assertion would notice if the line were wrong. Under agent-written tests, coverage pressure can produce execution-without-assertion. Mutation testing measures what coverage cannot: whether the suite kills deliberately injected bugs.
Proposal
Stryker (@stryker-mutator/vitest-runner) over packages/*/src:
- PR-scoped incremental runs (changed files only) as a CI job — fast enough to gate merges once tuned.
- Nightly full runs with a tracked mutation score; start by recording, then set the threshold at the observed baseline and ratchet upward (same policy as coverage: thresholds only ever tighten).
- Surviving mutants are work items: an agent picks a survivor, writes the killing test, repeats — a well-shaped autonomous loop.
- Equivalent mutants (provably behavior-preserving) get annotated exclusions with reasons, mirroring the
/* v8 ignore */policy.
Plan
- Add Stryker config scoped to one package (llm — smallest, most algorithmic) and measure runtime.
- Expand to all packages; record baseline scores in the config.
- Wire the nightly job; add the incremental PR job once runtime is acceptable.
Acceptance criteria
- A Stryker config runs over
packages/*/srcwith the vitest runner; a nightly job records the mutation score, and a ratcheting threshold fails the run when the score drops below the recorded baseline. - PR-scoped incremental runs gate merges once runtime is acceptable — or are explicitly kept nightly-only, with that outcome recorded here.
- Equivalent mutants carry annotated exclusions with reasons, mirroring the
/* v8 ignore */policy.
Risks
Runtime: mutation testing is expensive; per-file 100% coverage helps (every mutant is at least reached). If PR-scoped runs stay too slow, keep them nightly-only and rely on the score ratchet.