Files
deepseek-harness/docs/rfc/proposed/testing/2026-06-11-mutation-testing.md
Tianyi Cui 605587e79c docs(rfc): classify RFCs by kind via path-encoded subdirectories
Add a second axis to every RFC — its class (feature, bug-fix,
simplification, architecture, process, testing) — encoded in the path
as docs/rfc/{lifecycle}/{class}/file.md. The folder is the label, so
the closed set is enforced by structure rather than a parsed field.

Two new doc-sync gates back it:
- verify-rfc-classification: every RFC sits in a valid class folder and
  the README index lists it under the matching lifecycle→class heading.
- verify-doc-refs: every docs/*.md path cited in a packages|examples TS
  comment resolves — closes a drift class verify-md-links can't see, and
  catches the four comment refs this reorg moved.

The README gains a Classification section explaining the taxonomy and
per-class index sub-sections. A self-referential process RFC records why
the scheme is path-encoded and gated.
2026-06-20 22:29:45 +08:00

1.7 KiB

RFC: Mutation testing as the coverage counterweight

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

  1. Add Stryker config scoped to one package (llm — smallest, most algorithmic) and measure runtime.
  2. Expand to all packages; record baseline scores in the config.
  3. Wire the nightly job; add the incremental PR job once runtime is acceptable.

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.