zero-script-qa

# Zero Script QA Expert Knowledge

## Overview

Zero Script QA is a methodology that verifies features through **structured logs** and **real-time monitoring** without writing test scripts.

```
Traditional: Write test code → Execute → Check results → Maintain
Zero Script: Build log infrastructure → Manual UX test → AI log analysis → Auto issue detection
```

## Core Principles

### 1. Log Everything
- All API calls (including 200 OK)
- All errors
- All important business events
- Entire flow trackable via Request ID

### 2. Structured JSON Logs
- Parseable JSON format
- Consistent fields (timestamp, level, request_id, message, data)
- Different log levels per environment

### 3. Real-time Monitoring
- Docker log streaming
- Claude Code analyzes in real-time
- Immediate issue detection and documentation

---

## Logging Architecture

### JSON Log Format Standard

```json
{
  "timestamp": "2026-01-08T10:30:00.000Z",
  "level": "INFO",
  "service": "api",
  "request_id": "req_abc123",
  "message": "API Request completed",
  "data": {
    "method": "POST",
    "path": "/api/users",
    "status": 200,
    "duration_ms": 45
  }
}
```

### Required Log Fields

| Field | Type | Description |
|-------|------|-------------|
| timestamp | ISO 8601 | Time of occurrence |
| level | string | DEBUG, INFO, WARNING, ERROR |
| service | string | Service name (api, web, worker, etc.) |
| request_id | string | Request tracking ID |
| message | string | Log message |
| data | object | Additional data (optional) |

### Log Level Policy

| Environment | Minimum Level | Purpose |
|-------------|---------------|---------|
| Local | DEBUG | Development and QA |
| Staging | DEBUG | QA and integration testing |
| Production | INFO | Operations monitoring |

---

## Request ID Propagation

### Concept

```
Client → API Gateway → Backend → Database
   ↓         ↓           ↓          ↓
req_abc   req_abc     req_abc    req_abc

Trackable with same Request ID across all layers
```

### Implementation Patterns

#### 1. Request ID Generation (Entry Point)
```typescript
// middleware.ts
import { v4 as uuidv4 } from 'uuid';

export function generateRequestId(): string {
  return `req_${uuidv4().slice(0, 8)}`;
}

// Propagate via header
headers['X-Request-ID'] = requestId;
```

#### 2. Request ID Extraction and Propagation
```typescript
// API client
const requestId = headers['X-Request-ID'] || generateRequestId();

// Include in all logs
logger.info('Processing request', { request_id: requestId });

// Include in header when calling downstream services
await fetch(url, {
  headers: { 'X-Request-ID': requestId }
});
```

---

## Backend Logging (FastAPI)

### Logging Middleware

```python
# middleware/logging.py
import logging
import time
import uuid
import json
from fastapi import Request

class JsonFormatter(logging.Formatter):
    def format(self, record):
        log_record = {
            "timestamp": self.formatTime(record),
            "level": record.levelname,
            "service": "api",
            "request_id": getattr(record, 'request_id', 'N/A'),
            "message": record.getMessage(),
        }
        if hasattr(record, 'data'):
            log_record["data"] = record.data
        return json.dumps(log_record)

class LoggingMiddleware:
    async def __call__(self, request: Request, call_next):
        request_id = request.headers.get('X-Request-ID', f'req_{uuid.uuid4().hex[:8]}')
        request.state.request_id = request_id

        start_time = time.time()

        # Request logging
        logger.info(
            f"Request started",
            extra={
                'request_id': request_id,
                'data': {
                    'method': request.method,
                    'path': request.url.path,
                    'query': str(request.query_params)
                }
            }
        )

        response = await call_next(request)

        duration = (time.time() - start_time) * 1000

        # Response logging (including 200 OK!)
        logger.info(
            f"Request completed",
            extra={
                'request_id': request_id,
                'data': {
                    'status': response.status_code,
                    'duration_ms': round(duration, 2)
                }
            }
        )

        response.headers['X-Request-ID'] = request_id
        return response
```

### Business Logic Logging

```python
# services/user_service.py
def create_user(data: dict, request_id: str):
    logger.info("Creating user", extra={
        'request_id': request_id,
        'data': {'email': data['email']}
    })

    # Business logic
    user = User(**data)
    db.add(user)
    db.commit()

    logger.info("User created", extra={
        'request_id': request_id,
        'data': {'user_id': user.id}
    })

    return user
```

---

## Frontend Logging (Next.js)

### Logger Module

```typescript
// lib/logger.ts
type LogLevel = 'DEBUG' | 'INFO' | 'WARNING' | 'ERROR';

interface LogData {
  request_id?: string;
  [key: string]: any;
}

const LOG_LEVELS: Record<LogLevel, number> = {
  DEBUG: 0,
  INFO: 1,
  WARNING: 2,
  ERROR: 3,
};

const MIN_LEVEL = process.env.NODE_ENV === 'production' ? 'INFO' : 'DEBUG';

function log(level: LogLevel, message: string, data?: LogData) {
  if (LOG_LEVELS[level] < LOG_LEVELS[MIN_LEVEL]) return;

  const logEntry = {
    timestamp: new Date().toISOString(),
    level,
    service: 'web',
    request_id: data?.request_id || 'N/A',
    message,
    data: data ? { ...data, request_id: undefined } : undefined,
  };

  console.log(JSON.stringify(logEntry));
}

export const logger = {
  debug: (msg: string, data?: LogData) => log('DEBUG', msg, data),
  info: (msg: string, data?: LogData) => log('INFO', msg, data),
  warning: (msg: string, data?: LogData) => log('WARNING', msg, data),
  error: (msg: string, data?: LogData) => log('ERROR', msg, data),
};
```

### API Client Integration

```typescript
// lib/api-client.ts
import { logger }