2nd/10_Wiki/Topics/Green-Check-Mark-Syndrome.md

---
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: [[CI CD]]
- 변형: [[Test-Theater]]
- 응용: [[Mutation-Testing]] · [[Property-Based-Testing]] · [[Chaos-Engineering]]
- Adjacent: [[Goodharts-Law]] · [[Observability]]

## 🤖 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 |