[G1-Sync] Manual knowledge update

10_Wiki/Topics/Green-Check-Mark-Syndrome.md

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+---
+id: wiki-2026-0508-green-check-mark-syndrome
+title: Green Check Mark Syndrome
+category: 10_Wiki/Topics
+status: verified
+canonical_id: self
+aliases: [Green Check Syndrome, CI Theater, Test Theater]
+duplicate_of: none
+source_trust_level: A
+confidence_score: 0.9
+verification_status: applied
+tags: [anti-pattern, ci-cd, testing, observability]
+raw_sources: []
+last_reinforced: 2026-05-10
+github_commit: pending
+tech_stack:
+  language: TypeScript/Python
+  framework: GitHub-Actions/pytest
+---
+
+# Green Check Mark Syndrome
+
+## 매 한 줄
+> **"매 green CI ≠ correct system."** 매 anti-pattern: 매 passing tests 의 confidence inflation, 매 actual coverage / assertion strength / production behavior 의 disconnect. 매 2026 prevalent — 매 LLM-generated tests, 매 mock-heavy suites, 매 flaky-retry hides 매 real bugs.
+
+## 매 핵심
+
+### 매 Symptoms
+- 매 100% green builds, 매 still production incidents 의 frequent.
+- 매 tests assert truisms (`expect(1).toBe(1)`).
+- 매 mocks return canned data — 매 integration paths 의 untested.
+- 매 retries hide flakiness — 매 race conditions 의 ignored.
+- 매 coverage % high, 매 mutation score low.
+
+### 매 Root causes
+- **Goodhart's law**: 매 green check 의 metric → metric 의 target → 매 gamed.
+- **Mock theater**: 매 unit isolation 의 over-mocked, 매 real failure modes 의 missed.
+- **AI-generated tests**: 매 LLM이 매 implementation을 매 mirror — 매 same bug 의 test에도 present.
+- **Flaky-retry culture**: 매 "retry until green" 의 normalized.
+
+### 매 Detection
+- Mutation testing — 매 assertion strength measurement.
+- Property-based testing — 매 input space coverage.
+- Production observability — 매 errors in prod that tests 의 missed.
+- Test-impact analysis — 매 untouched code paths surface.
+
+### 매 응용
+1. CI quality dashboard — 매 mutation score + flake rate.
+2. Test review checklist — 매 each test 의 specific failure mode가 매 catch?
+3. Chaos engineering — 매 production-like failures inject.
+
+## 💻 패턴
+
+### Mutation testing (Stryker)
+```javascript
+// stryker.conf.json
+{
+  "mutate": ["src/**/*.ts"],
+  "testRunner": "vitest",
+  "thresholds": { "high": 80, "low": 60, "break": 50 }
+}
+```
+
+```bash
+npx stryker run
+# 매 surviving mutants 의 매 weak tests indicate
+```
+
+### Property-based test
+```typescript
+import { fc } from 'fast-check';
+
+test('reverse twice = identity', () => {
+  fc.assert(
+    fc.property(fc.array(fc.integer()), (arr) => {
+      expect(reverse(reverse(arr))).toEqual(arr);
+    })
+  );
+});
+```
+
+### Flake-detector (no silent retry)
+```yaml
+# .github/workflows/test.yml
+- name: Test
+  run: npm test
+  # NO retry — 매 flake 의 immediately surface
+- name: Flake report
+  if: failure()
+  run: |
+    echo "::warning::Test failed — investigate, do not retry blindly"
+```
+
+### Assertion-strength linter
+```python
+# detect weak assertions
+import ast
+from pathlib import Path
+
+WEAK_PATTERNS = {'assertTrue(True)', 'assertEqual(1, 1)', 'assert True'}
+
+for file in Path('tests').rglob('*.py'):
+    tree = ast.parse(file.read_text())
+    for node in ast.walk(tree):
+        if isinstance(node, ast.Call) and ast.unparse(node) in WEAK_PATTERNS:
+            print(f"WEAK: {file}:{node.lineno}")
+```
+
+### Production-trace replay
+```python
+# 매 prod traces → test fixtures
+import json
+from opentelemetry.trace import get_tracer
+
+def replay_prod_trace(trace_id: str):
+    trace = fetch_trace(trace_id)  # from observability backend
+    inputs = extract_inputs(trace)
+    result = run_system(inputs)
+    expected = trace.outputs
+    assert result == expected, f"Drift from prod: {trace_id}"
+```
+
+### Real integration (no mocks)
+```typescript
+// testcontainers — 매 real DB
+import { GenericContainer } from 'testcontainers';
+
+let pg: StartedTestContainer;
+beforeAll(async () => {
+  pg = await new GenericContainer('postgres:17')
+    .withExposedPorts(5432)
+    .withEnvironment({ POSTGRES_PASSWORD: 'test' })
+    .start();
+});
+
+test('real query', async () => {
+  const client = connect(pg.getMappedPort(5432));
+  await client.query('CREATE TABLE u (id int)');
+  // 매 real SQL behavior tested
+});
+```
+
+## 매 결정 기준
+| 상황 | Approach |
+|---|---|
+| New test suite | Property-based + integration |
+| Existing green-but-fragile suite | Mutation testing audit |
+| Flaky test | Investigate root cause, never blind-retry |
+| Mock-heavy suite | Add testcontainers for real I/O |
+| Coverage-driven culture | Switch metric to mutation score |
+
+**기본값**: 매 green CI 의 trust 의 X — 매 mutation score + 매 prod observability + 매 chaos drills 의 combined signal.
+
+## 🔗 Graph
+- 부모: [[Software-Anti-Patterns]] · [[CI-CD]]
+- 변형: [[Test-Theater]] · [[Coverage-Gaming]] · [[Mock-Theater]]
+- 응용: [[Mutation-Testing]] · [[Property-Based-Testing]] · [[Chaos-Engineering]]
+- Adjacent: [[Goodharts-Law]] · [[Observability]] · [[Flaky-Tests]]
+
+## 🤖 LLM 활용
+**언제**: test review (assertion strength critique), mutation report triage, prod-trace replay generation.
+**언제 X**: 매 LLM이 매 test generation 단독 — 매 same blind spots reproduce.
+
+## ❌ 안티패턴
+- **Coverage as quality**: 매 100% line coverage, 매 0% mutation kill rate.
+- **Auto-retry on fail**: 매 race condition 의 hide → prod incident.
+- **Mock everything**: 매 unit "passes", 매 integration broken.
+- **LLM-only test suite**: 매 implementation mirror — 매 bug parity.
+
+## 🧪 검증 / 중복
+- Verified (Hillel Wayne "Test theater", Google Testing Blog "Just Say No to More End-to-End Tests").
+- 신뢰도 A.
+
+## 🕓 Changelog
+| 날짜 | 변경 |
+|---|---|
+| 2026-05-08 | Phase 1 |
+| 2026-05-10 | Manual cleanup — CI theater anti-pattern, mutation testing, real integration |