Ziya
2565133af3
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）。
37 lines
2.1 KiB
Markdown
37 lines
2.1 KiB
Markdown
# RFC: Mutation testing as the coverage counterweight
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English | [中文](2026-06-11-mutation-testing.zh.md)
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Status: proposed
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## Problem
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The per-file 100% coverage gate ([the quality-gates decision](../../implemented/process/2026-06-11-quality-gates.md)) 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.
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## Proposal
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Stryker (`@stryker-mutator/vitest-runner`) over `packages/*/src`:
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- **PR-scoped incremental runs** (changed files only) as a CI job — fast enough to gate merges once tuned.
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- **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).
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- Surviving mutants are work items: an agent picks a survivor, writes the killing test, repeats — a well-shaped autonomous loop.
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- Equivalent mutants (provably behavior-preserving) get annotated exclusions with reasons, mirroring the `/* v8 ignore */` policy.
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## Plan
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1. Add Stryker config scoped to one package (llm — smallest, most algorithmic) and measure runtime.
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2. Expand to all packages; record baseline scores in the config.
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3. Wire the nightly job; add the incremental PR job once runtime is acceptable.
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## Acceptance criteria
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- A Stryker config runs over `packages/*/src` with 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.
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- PR-scoped incremental runs gate merges once runtime is acceptable — or are explicitly kept nightly-only, with that outcome recorded here.
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- Equivalent mutants carry annotated exclusions with reasons, mirroring the `/* v8 ignore */` policy.
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## Risks
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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.
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<!-- rfc-format: alternatives-not-recorded (pre-format RFC) -->
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