dev-testing

name	dev-testing
description	MUST USE for testing, QA, regression protection, and release verification — unit, integration, API, contract, Playwright E2E, CI, security-scan, coverage, and TDD strategy. Triggers: write tests, regression test, Playwright, E2E, contract test, coverage, CI flake, TDD, test, testing, QA, 테스트, 회귀 테스트, 품질 게이트.
metadata	{"short-description":"Testing and QA router: strategy, harness choice, CI gates, TDD, and coverage.","keywords":"test, testing, TDD, coverage, regression, e2e, playwright, contract test, CI, property-based, mutation","last-verified":"2026-07-02"}

Testing & QA

Balance: ~40% Backend/API, ~40% Frontend/E2E (Playwright), ~20% Cross-cutting (CI, Security, TDD, Coverage) -- directional guidance, not a hard ratio. Scope: test harnesses, fixtures, mock policy, runners, Playwright, CI gates, coverage. Root-cause analysis and debugging playbooks → dev-debugging. This skill activates by change surface when work needs verification depth, regression coverage, or a reproducible test harness.

C0/C1 work (small local patches): See dev §0.0 Work Classifier + §0.1 Patch Fast-Path before reading references.

Modular References

File	When to Read	What It Covers
references/core/crud-test-matrix.md	When choosing verification depth for a classified task, or testing a CRUD slice	Risk-tier minimums, per-operation negatives, UI smoke rule
references/edge-first-testing.md	New unit/service/integration tests for features (skip for regression/contract tests)	Edge-first principle, test order by change type, 11-class edge matrix
references/backend-testing.md	Backend/API testing	Supertest patterns, DB fixtures, auth mocking
references/ci-pipeline.md	CI configuration	GitHub Actions, gates, caching, parallelism
references/load-testing.md	Performance/load testing, C3+ production readiness	k6/Locust, test types, measure→profile→verify, CI gates
references/ml-evaluation.md	ML model/LLM evaluation, quality gates	LLM-as-judge, RAGAS, DeepEval, CI eval gate, regression detection. CI eval gates are dataset-versioned + regression-based: pin prompts/models/retrieval config, preserve traces, calibrate judges on golden examples, fail only on meaningful regressions or safety failures

When tests depend on current external API behavior, provider docs, CI service behavior, test-environment versions, dependency audit evidence, or recorded mock/fixture sources, read the active search skill and follow its source-fetch and evidence-status rules.

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1. Test Strategy

1.1 Models

Model	Best For	Emphasis
Test Pyramid	monoliths, libraries	speed, isolation
Testing Trophy	modern web apps, REST backends	confidence-to-cost
Test Honeycomb	microservices, async systems	boundary verification

1.2 Recommended Trophy Distribution

Layer	Default Share	Typical Tools
Static analysis	base layer	tsc, ESLint, mypy, Ruff
Unit	~25%	Vitest, Jest, pytest
Integration	~50%	Supertest, httpx, Testcontainers
Contract	~10%	Pact, OpenAPI validators, Schemathesis
E2E	~10%	Playwright
Manual / exploratory	~5%	human review

1.3 Risk-First Priorities

1. auth / session / permission boundaries
2. money movement, quota, credits
3. data mutation and irreversible actions
4. file upload / parsing / external webhooks
5. shared API contracts used by frontend clients
6. error paths, retries, rollback behavior

1.4 Harness Selector

Problem	Primary Harness	Avoid
pure business rule	unit / service test	browser test
route + middleware + serialization	API integration test	mocking the route itself
DB query / migration / transaction	real DB integration test	fake repository for SQL correctness
frontend consuming backend JSON	contract test	manual-only verification
rendered critical flow	Playwright smoke	asserting internal React state
rendered artifact (visual correctness)	render-grounding loop (dev-pabcd C-RENDER-GROUNDING-01)	static parse / tsc alone

1.5 General Rules

• Write tests for new features, bug fixes, refactors, and behavior changes.
• Prefer one behavioral concern per test.
• Use factories / builders for setup; avoid repeated inline blobs.
• A fast real dependency beats a mock. A mock beats an untested branch.
• If the failure is mysterious, delegate methodology to dev-debugging, then return here for the regression harness.
• STRICT (TEST-ANTI-FLAKE-01): A time-based flake is a bug. Do not use sleep-based synchronization, retry-as-fix, or green-on-retry acceptance without a deterministic cause and harness correction.
• Verification depth follows dev §3 DEV-VERIFY-FLOOR-01; CRUD per-operation negative coverage is owned by references/core/crud-test-matrix.md.

1.5a Limited-Oracle / Score-Objective Evaluation

When the real evaluator is scarce, paid, rate-limited, or opaque and local tests are proxy metrics for a score/objective, apply §9.5 (single owner of GATE-ORACLE-VALIDITY-01, GATE-PREFIX-HORIZON-01, GATE-INVARIANT-EV-01, GATE-HOLDOUT-LEAKAGE-01, GATE-AGREEMENT-STATS-01). Pairs with dev-pabcd §10 Optimization-Loop Meta-Rules.

1.6 Property-Based & Mutation Testing (verified 2026-07-02)

Technique	Use for	Default tools	When
Property-based	Pure logic, parsers, serializers, state machines, API invariants	fast-check (TS), Hypothesis (Python)	DEFAULT for invariant-heavy code
Mutation	Judging test-suite strength on critical domain logic, validators, security branches	Stryker (JS/TS), mutmut (Python)	Selective, after stable unit/property tests — not every PR

• Vitest 4 is the current runner baseline: Browser Mode is stable (visual regression via toMatchScreenshot, Playwright trace generation, expect.schemaMatching).

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2. Backend & API Testing

Deep reference: references/backend-testing.md

2.1 Coverage Map

Layer	Verify	TypeScript Default	Python Default
Service layer	validation, orchestration, domain errors	Vitest	pytest
API layer	status, envelope, middleware, auth	Supertest	httpx / ASGITransport
Repository layer	SQL / ORM correctness	Testcontainers + real DB	Testcontainers + real DB
Background jobs	idempotency, retry, dead-letter	Vitest + fake clock	pytest + monkeypatch

2.2 Mock Strategy Hierarchy

real deterministic dependency
→ Testcontainers / ephemeral infra
→ recorded responses / thin fake
→ manual stub / fake
→ framework mock as last resort

2.3 Service & API Patterns

Mock dependencies at service boundaries. Use Supertest/httpx for route-level integration tests. Match response envelope shape from backend contracts.

2.4 Database Truth with Testcontainers

Use a real database when verifying migrations, transactions, unique constraints, foreign keys, query translation, and performance-sensitive SQL. Use Testcontainers for real DB truth in correctness-sensitive persistence tests. Start container in beforeAll/fixture setup, capture connection URI.

2.5 Fixture / Seed Synchronization

• Prefer builders / factories over copied JSON snapshots.
• Keep shared contract examples in fixtures/contracts/ or equivalent.
• Seed data should expose stable IDs used by Playwright smoke flows.
• If frontend mocks drift from backend fixtures, write or update a contract test first.

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3. Contract Testing

Contract tests protect the frontend↔backend boundary. They sit between API tests and browser tests. Rule: Playwright proves the experience. Contract tests prove the shared shape.

3.1 Contract-Stable Surface

• response envelope: success, data, error, meta
• error taxonomy: HTTP status + machine-readable error.code
• pagination fields, auth headers, cookie behavior
• requestId propagation
• nullability, timestamps, enums, money serialization

3.2 Contract Options

Style	Best For	Tooling
consumer-driven contract	rapidly changing frontend/backend teams	Pact
schema-first contract	OpenAPI-led backends	OpenAPI validators, Schemathesis
type-level contract	TS monorepos	shared types / codegen
full-stack smoke	final user confidence	Playwright

3.3 Consumer Contract — TypeScript (Pact / PactV4)

PactV4 (aliased Pact) is the current interface and supports Pact Specification v4; treat PactV3 as the legacy spec-v3 API. Workflow:

1. Define interaction: provider state + request + expected response (matchers for flexible matching)
2. Execute test against Pact mock server
3. Assert consumer expectations
4. Pact file auto-writes to pacts/ → publish to broker → provider verifies

See references/backend-testing.md for a full example.

3.4 Schema Verification

Use schema-based API testing (Schemathesis) to verify OpenAPI/GraphQL contract compliance. (Dredd is legacy/inactive — do not adopt for new projects.)

3.5 Rules

• Contract tests are strongly recommended for parallel FE/BE, public APIs, and cross-team contracts.
• E2E success does not replace provider verification.
• Store golden examples near the contract, not inside one app only.
• If the shape is intentionally breaking, update the contract first, then all consumers.

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4. Playwright Browser Testing

Use Playwright after API and contract tests are already trustworthy. Browser tests should validate rendered flows, accessibility-critical interactions, and real integration seams that lower layers cannot prove alone. Helper Scripts Available:

• scripts/with_server.py - Manages server lifecycle (supports multiple servers) Run scripts with --help first — treat as black boxes to avoid context window pollution.

4.1 Decision Tree: Choosing Your Approach

User task → Static HTML? → Read file → find selectors → write Playwright script
         → Dynamic app? → Server running? → No: `python scripts/with_server.py --help`
                                           → Yes: Recon-then-action (navigate → screenshot → selectors → act)

4.2 Example: Using with_server.py

# Single server:
python scripts/with_server.py --server "npm run dev" --port 5173 -- python your_automation.py

# Multiple servers:
python scripts/with_server.py \
  --server "cd backend && python server.py" --port 3000 \
  --server "cd frontend && npm run dev" --port 5173 \
  -- python your_automation.py

4.3 Reconnaissance-Then-Action Pattern

1. Wait for an explicit app-ready signal or locator assertion → 2. Screenshot/inspect DOM → 3. Identify selectors → 4. Execute actions

4.4 Best Practices

• Use bundled scripts as black boxes — run --help first, invoke directly.
• Use sync_playwright() for synchronous scripts; always close the browser.
• Prefer locator-based interactions and web-first assertions: expect(page.get_by_role("button", name="Save")).to_be_visible(), then click() on that locator.
• Prefer user-facing locators, especially get_by_role() with an accessible name. Use get_by_label(), get_by_placeholder(), or get_by_test_id() when role/name cannot express the target.
• Avoid networkidle, hard sleeps, and wait_for_timeout() in tests. Wait on observable app-ready signals, locator actions, or expect() assertions.
• AI-authored tests (DEFAULT): Playwright MCP / Test Agents (planner/generator/healer) are generation-and-repair aids only — final acceptance still requires deterministic locators, web-first assertions, traces, and a human-readable failure artifact.

4.5 Reference Files

• examples/ - Examples showing common patterns:
  • element_discovery.py - Discovering buttons, links, and inputs on a page
  • static_html_automation.py - Using file:// URLs for local HTML
  • console_logging.py - Capturing console logs during automation

4.6 Browser Testing Rules

• Run contract tests and API tests first for broken-data bugs.
• Use Playwright for rendered truth, not as a replacement for service tests.
• Prefer one smoke flow per critical path over many brittle micro-flows.
• If a failure looks like data-shape drift, go back to §2 Backend & API Testing or §3 Contract Testing.

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5. CI Pipeline Integration

Full workflow templates: references/ci-pipeline.md

5.1 Pipeline Order

quality (lint / typecheck)
→ unit + integration tests
→ contract tests
→ Playwright E2E
→ security scan
→ coverage aggregation + artifacts

5.2 Pipeline Template

Structure CI jobs in dependency chain: quality → backend-tests → contract-tests → e2e

Key configuration:

• concurrency.cancel-in-progress: true — avoid wasted runs
• strategy.fail-fast: false — for matrix builds
• Shard large suites: --shard=${{ matrix.shard }}/N
• Install Playwright deps: npx playwright install --with-deps chromium

See references/ci-pipeline.md for full GitHub Actions and GitLab CI templates.

5.3 Matrix & Parallelization

Dimension	When to Use
Node / Python version matrix	packages, SDKs, shared libraries
OS matrix	native modules, CLI behavior
shard matrix	large suites exceeding CI budget

npx vitest run --shard=1/4
npx playwright test --shard=1/4 --workers=4
pytest -n auto --dist=loadgroup

5.4 Flaky Test Remediation

Symptom	First Fix
passes locally, fails in CI	deterministic seeds, containerized deps, explicit waits
order-dependent failure	reset shared state in fixtures
green on retry only	remove wall-clock / random assumptions
screenshot noise	stable CI image, mask dynamic regions
Protocol: detect → quarantine if blocking → assign owner → reinstate after repeated green runs.

5.5 Rules

• Do not let Playwright be the only blocking job.
• Contract tests should run before browser tests.
• Upload artifacts for failures: coverage, junit, traces, screenshots.
• Fail the build on broken thresholds, not only test exit codes.

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6. TDD Enforcement Mode

When ENFORCE_TDD=true is set in project instructions or explicitly requested, this section becomes mandatory.

6.1 RED → GREEN → REFACTOR

1. RED — write the failing test first and verify it fails for the right reason.
2. GREEN — write the minimum implementation to pass.
3. REFACTOR — clean up after green, then rerun the affected suite.

6.2 Self-Audit Checklist

Check	Pass Criteria
Test written before implementation?	test file added / updated before or with code
Failure observed before fix?	red state was actually executed
Behavior-focused assertions?	checks outputs, side effects, contracts
Regression locked in?	failing case is now protected by a persistent test

6.3 Vertical Tracer-Bullet TDD

Prefer one behavior test → minimal implementation → next behavior. Slice by something a user, caller, or consuming module can observe, not by horizontal layers such as "DB", "API", then "UI". Assert through public interfaces and durable contracts. Retire shallow scaffolding tests when a stronger interface or acceptance test covers the same promise.

6.4 Default Style

Style	Best For
London / mockist	orchestration-heavy boundaries
Chicago / classicist	domain logic and transforms
Hybrid	most production code
Default to Hybrid: mock external systems, keep internal collaboration real unless it becomes too slow or unstable.

6.5 Boundary with dev-debugging

• dev-testing owns the regression harness and enforcement loop.
• dev-debugging owns root-cause methodology once a failure is mysterious or multi-layered.
• After dev-debugging isolates the cause, come back here to lock it in with tests.

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6.6 AI-Assisted Development Regressions

When an AI writes and reviews its own code, it carries the same assumptions into both steps. Automated tests break this feedback loop.

Common AI Regression Patterns

Pattern	Description	Test Strategy
Sandbox/production mismatch	Fix applied to one code path, not both	Assert same response shape in both modes
SELECT clause omission	New field in response but missing from DB query	Assert all required fields are present and defined
Error state leakage	Error set but stale data not cleared	Assert state cleanup on error transitions
Missing rollback	Optimistic UI update without recovery on failure	Assert state restoration after simulated API error

Regression Naming Convention

Name regression tests with BUG-R{N} convention. Assert all required fields with a loop.

Sandbox-Mode API Testing

When the project supports a sandbox/mock mode, use it for fast DB-free regression testing:

• Force sandbox mode in test setup: process.env.SANDBOX_MODE = 'true'
• Assert sandbox responses match the same contract as production responses.
• Treat sandbox/production parity as a high-priority regression target.
• In sandbox/spike mode, write tests for bugs found — coverage grows organically. For production refactors, see §1.5 (tests required for behavior changes).

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6.7 Test-Induced Production Defense Detection

Rule: Do not add production defensive code solely to satisfy unrealistic tests. A production guard is allowed only when the invalid state can occur at a real boundary or represents an explicit domain rule.

Production change smell	Likely test problem	Required action
Internal if (!x) return added after unit test fails	Test fixture omitted required field	Fix fixture factory or test boundary validation
Required field made optional to satisfy test	Test is using invalid domain object	Restore required type and update test data
Catch-all added so test passes	Test expects silence instead of failure	Assert typed error or user-visible failure
Production default added for impossible state	Test bypassed constructor/parser	Use real constructor/parser in test
Private helper exported only for test	Test is coupled to implementation	Test public behavior or move helper to test support
Sleep/retry added only for test flake	Test lacks deterministic synchronization	Wait on observable condition or fake clock
NODE_ENV === "test" branch added	Test-only production behavior	Remove branch; improve test harness

Required questions before adding a guard:

1. Is the input from an untrusted boundary? → If yes, validate at that boundary
2. Can this state happen in production? → If no, fix the test
3. What contract allows this value? → Cite schema/type/domain rule
4. Would this hide a real bug? → If yes, fail fast instead

Banned patterns: process.env.NODE_ENV === "test" branches, silent fallbacks for impossible internal state, making required types optional for mocks, exporting internals only for tests.

Allowed guards: Boundary validation (process/network/user/file boundary), backward compatibility (documented old schema), security checks, domain invariants, observed production bug regressions, external dependency adapters.

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7. Accessibility Testing

Component Level

• jest-axe / vitest-axe: run axe-core on rendered components

  import { axe, toHaveNoViolations } from 'jest-axe'
  expect.extend(toHaveNoViolations)
  expect(await axe(container)).toHaveNoViolations()
  

Page Level

• Playwright a11y assertions:

  import AxeBuilder from '@axe-core/playwright'
  const results = await new AxeBuilder({ page }).analyze()
  expect(results.violations).toEqual([])
  

CI Pipeline

• Gate order (verified 2026-07-02): component axe (jest-axe/vitest-axe) → page axe (@axe-core/playwright) → keyboard/focus/manual checks. Blocking gate = zero serious/critical axe violations + targeted manual checks.
• Lighthouse a11y score (≥90) is an advisory route-level smoke signal, NOT the blocking gate — Lighthouse itself separates automated scoring from required manual checks.
• Pa11y: page-level scanning for WCAG AA violations
• Run a11y tests on EVERY page route, not just the homepage

Observability Verification

Verify trace propagation in integration tests. Assert that spans appear for critical paths. Check structured log format matches the schema in dev-backend/references/core/observability.md.

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8. Security Testing

→ Delegated: threat modeling and secure design policy belong to dev-security. This section covers the automated test hooks and CI gates that enforce those rules.

8.1 Minimum Security Stack

fast local checks
→ Semgrep / CodeQL gate
→ dependency audit
→ auth / validation regression tests

8.2 Dependency Scanning Commands

npm audit --audit-level=high
pip-audit --strict --desc

8.3 Semgrep Gate

The returntocorp/semgrep-action wrapper is deprecated (stated by the repo itself) — run Semgrep natively in CI:

semgrep:
  runs-on: ubuntu-latest
  container: semgrep/semgrep
  steps:
    - uses: actions/checkout@v4
    - run: semgrep ci --config p/default --config p/javascript --config p/typescript --config p/python

(Open-source alternative engine: Opengrep, the LGPL-2.1 community fork — see dev-security/references/static-analysis.md.)

8.4 Security Regressions

Test missing auth (expect 401) and verify error.code matches contract for every auth-protected endpoint.

8.5 Rules

• dependency audit in CI
• Semgrep or equivalent SAST
• auth / permission regression tests
• validation tests for malicious or malformed input
• a blocking rule for high / critical dependency findings

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9. Coverage & Quality Gates

9.1 Suggested Thresholds

These are project/risk-based, not universal minimums. Adjust for your context.

Metric	Suggested Floor	Ideal
Line coverage	70%	85%+
Branch coverage	60%	80%+
Function coverage	80%	90%+
Diff coverage	80%	90%+

9.2 Outcome Metrics

Metric	Target
Defect detection rate	> 80%
Mean time to detect	< 1 CI run
Test signal-to-noise	> 95%
Contract drift rate	near 0

9.3 Coverage Workflow

1. generate coverage reports

   npm test -- --coverage
   npx vitest run --coverage
   pytest --cov --cov-report=xml
   

2. review by priority: auth, payment, mutations, upload, contracts first
3. write targeted tests for the gaps
4. publish artifacts and fail the merge when thresholds drop

9.4 Quality Gate Checklist

• focused unit / service tests
• API integration tests for changed routes
• contract tests for shared payload changes
• Playwright smoke for critical rendered journeys
• security scan / dependency scan
• coverage thresholds and diff coverage
• CI artifacts uploaded for failure analysis

9.5 Limited-Oracle / Score-Objective Evaluation

Use these rules when the true evaluator is scarce, paid, rate-limited, or opaque and local checks are only proxy metrics for a score/objective. PABCD loop response to repeated candidate deaths is owned by dev-pabcd §10 Optimization-Loop Meta-Rules.

• STRICT (GATE-ORACLE-VALIDITY-01): When the true evaluator/oracle is rate-limited (limited submissions, paid runs) and local metrics are proxies, evaluator validity is a prerequisite gate. Before trusting the proxy for accept/reject, quantify historical divergence: cases where the proxy said better/equal but the oracle said worse. A proxy with known optimistic bias must not be the sole acceptance evidence.
• DEFAULT (GATE-PREFIX-HORIZON-01): Replay-based evidence (recorded logs, scripted opponents) is prefix-valid only; it stops being valid when the candidate diverges from the recorded trajectory. Candidates that diverge early need live adversarial evaluation through a modeled opponent/environment, not replays. State the divergence turn/point when citing replay evidence.
• DEFAULT (GATE-INVARIANT-EV-01): Every hard invariant in an acceptance gate (a metric that must not regress) needs an expected-value justification: protected value versus the candidate-space it vetoes. If a hard invariant vetoes 3+ consecutive candidates that target strictly larger gains, downgrade it to a soft cost and re-justify or remove.
• DEFAULT (GATE-HOLDOUT-LEAKAGE-01): Fixed evaluation sets become training data under adaptive reuse. Rotate or quarantine repeatedly used sets, keep a blind final set, and treat repeated score-driven tuning on the same instances as leakage risk. Grounding: Blum and Hardt, "The Ladder: A Reliable Leaderboard for Machine Learning Competitions" (arXiv:1502.04585), and Dwork et al., "The reusable holdout: Preserving validity in adaptive data analysis" (arXiv:1506.02629).
• HEURISTIC (GATE-AGREEMENT-STATS-01): For proxy-vs-oracle validation, report agreement statistics that expose error shape: sign-discordance, bias, and worst-case error. Correlation alone is not enough; Bland-Altman style agreement analysis is the grounding model.

Grounding: observed in a 14-discard optimization plateau where a prefix-only replay gate and a hard draw-protection invariant locked a 3.5/8 score.

10. Pre-Flight Test Checklist

10.1 Change-Type Routing

• pure business logic change → add / update unit or service tests
• API or middleware change → add / update API integration tests
• shared frontend↔backend payload change → add / update contract tests
• rendered user flow change → add / update Playwright smoke coverage
• auth / upload / billing / external integration change → add security or edge-case regression coverage

10.2 Harness Readiness

• fixtures are deterministic and reusable
• real dependencies are used where correctness matters
• Testcontainers are used for DB truth, not mocked SQL
• external APIs are mocked or recorded intentionally, not accidentally called live
• ENFORCE_TDD requirements were followed if enabled

10.3 Contract & Data Integrity

• response envelope remains stable or contract was updated first
• error codes are asserted, not only HTTP status
• requestId, pagination, and nullability are verified where relevant
• frontend fixtures do not drift from backend examples

10.4 CI & Reporting

• relevant CI jobs exist and are actually executed
• sharding / matrix choices match project size
• flaky failures were investigated instead of blindly retried
• coverage / junit / trace artifacts are available on failure

10.5 Final Rule (risk-tier)

Verification intensity follows the work class (dev §0.0 / references/core/crud-test-matrix.md): for C2 UI work, one focused smoke (manual click-through or one Playwright run) plus targeted checks IS a complete story; for C3/C4 or release-sensitive work, a single smoke is not enough — run the affected suites and required negatives. Manual/Playwright smoke is a risk-tier rule, not a universal blocker.

unit / service
→ API integration
→ contract verification
→ Playwright smoke
→ CI gate + coverage + security scan