[Testing 21] test depth: mutation testing + SSE load harness (on-demand) - #254
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[Testing 21] test depth: mutation testing + SSE load harness (on-demand)#254amal66 wants to merge 1 commit into
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Two on-demand depth tools, neither a merge gate: - Stryker mutation testing scoped to the security-critical backend libs (access.ts, downloadTokens.ts, safeError.ts, chat/citations.ts). Measured 74.0-76.4% mutation score across runs; thresholds.break=69 fails only on real regressions. `npm run test:mutation` locally (~3 min), .github/workflows/mutation.yml on demand + monthly cron, HTML report uploaded as artifact. - k6 load harness for the SSE chat stream (loadtest/sse-stream.js): ramps to N concurrent POST /chat streams, checks TTFB and that every stream delivers events through to the [DONE] sentinel — the past incident class (streams timing out on long tool calls). Lenient, documented thresholds. .github/workflows/loadtest.yml is workflow_dispatch-only and boots nothing: point it at a staging stack (PR Open-Legal-Products#210). docs/test-depth.md explains how to read the mutation report, how to run the k6 harness against the local stack, and why neither gates merges. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
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Two tools that go a level deeper than the regular test suite. Neither one gates merges — both are run-on-demand, so they cost you nothing day to day.
1. Mutation testing for the security-critical code. Line coverage says a test ran a line; it doesn't say a test would notice if that line's behavior changed. Mutation testing checks exactly that: Stryker plants hundreds of small deliberate bugs (flip a comparison, delete an early return, weaken a regex) and re-runs the suite for each one. Any bug the suite doesn't catch is listed as "survived" — a concrete missing assertion. It's scoped to the four places where a hollow test would be dangerous: sharing/access checks (
access.ts), signed download tokens (downloadTokens.ts), secret redaction (safeError.ts), and citation extraction (chat/citations.ts). Current score: ~74–76% of planted bugs caught; the run fails only if that drops below 69, so it flags real regressions, not noise. Run it withcd backend && npm run test:mutation(~3 min) or from the Actions tab; a monthly scheduled run catches slow drift. The HTML report shows each surviving mutant inline in the code — the survivingsafeErrorredaction-regex mutants are ready-made test cases for whoever wants a small follow-up PR.2. A load test for chat streaming. The SSE stream behind
POST /chatis the hot path and has caused incidents before (streams timing out during long tool calls).loadtest/sse-stream.js(k6) ramps up to N simultaneous chat streams and verifies each one starts quickly and actually runs to completion ([DONE]arrives) — with deliberately lenient, documented thresholds: a red run means "streams are hanging," not "we missed an SLO we never set." Run it locally perdocs/test-depth.md, or via the manual SSE load test workflow, which boots nothing itself — you point it at an already-running staging stack (the one from #210 is the intended target) and store a test user's token in theLOADTEST_AUTH_TOKENsecret. Never point it at production: it creates real chats and burns real tokens.Why not merge gates? Mutation testing multiplies test runtime; the load test needs a live stack with real keys. Both are too slow/stateful to put in front of every PR, and a flaky required check is worse than none. If the project gains contributors and a permanent staging stack, the natural upgrade path is in
docs/test-depth.md.Verified: two full local Stryker runs completed green (2m51s / 2m25s); k6 script validated via
k6 inspect+ a dry run in docker; both workflows YAML-parse. Lockfile changes are npm-generated (npm install, never hand-edited).🤖 Generated with Claude Code