NestJS: Polishing and testing

🎯 Mục tiêu tuần cuối: Hoàn thiện ứng dụng, viết tests, documentation, và có thể demo/giải thích toàn bộ

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1. CHỨC NĂNG CẦN HOÀN THÀNH

STT	Chức năng	Mô tả	Output
6.1	Error Handling	Global exception filters	Errors được handle gracefully
6.2	Unit Tests	Test services, scoring	Coverage > 80%
6.3	Integration Tests	Test API endpoints	All endpoints tested
6.4	E2E Tests	Test WebSocket flow	Full game flow tested
6.5	Swagger Docs	API documentation	/api-docs accessible
6.6	Graceful Shutdown	Handle SIGTERM	Clean disconnect

---

2. KIẾN THỨC CẦN NẮM VỮNG

2.1 Error Handling Patterns

📖 HTTP Exception Filters

// Global exception filter
import {
  ExceptionFilter,
  Catch,
  ArgumentsHost,
  HttpException,
  HttpStatus,
  Logger,
} from '@nestjs/common';

@Catch()
export class AllExceptionsFilter implements ExceptionFilter {
  private readonly logger = new Logger('ExceptionFilter');

  catch(exception: unknown, host: ArgumentsHost) {
    const ctx = host.switchToHttp();
    const response = ctx.getResponse();
    const request = ctx.getRequest();

    const status =
      exception instanceof HttpException
        ? exception.getStatus()
        : HttpStatus.INTERNAL_SERVER_ERROR;

    const message =
      exception instanceof HttpException
        ? exception.message
        : 'Internal server error';

    this.logger.error(
      `${request.method} ${request.url} - ${status}: ${message}`,
      exception instanceof Error ? exception.stack : '',
    );

    response.status(status).json({
      statusCode: status,
      timestamp: new Date().toISOString(),
      path: request.url,
      message,
    });
  }
}

// main.ts
app.useGlobalFilters(new AllExceptionsFilter());

📖 WebSocket Exception Handling

import { Catch, ArgumentsHost } from '@nestjs/common';
import { BaseWsExceptionFilter, WsException } from '@nestjs/websockets';

@Catch(WsException)
export class WsExceptionFilter extends BaseWsExceptionFilter {
  catch(exception: WsException, host: ArgumentsHost) {
    const client = host.switchToWs().getClient();
    const error = exception.getError();
    
    client.emit('exception', {
      status: 'error',
      message: typeof error === 'string' ? error : error['message'],
    });
  }
}

// Throwing WsException
@SubscribeMessage('joinRoom')
handleJoinRoom(@MessageBody() data: any) {
  if (!data.pin) {
    throw new WsException('PIN is required');
  }
}

---

2.2 Testing in NestJS

📖 Test Pyramid

         ╱╲
        ╱  ╲
       ╱ E2E╲         ← Ít nhất, chậm nhất, UI tests
      ╱──────╲
     ╱Integration╲    ← API endpoints, database
    ╱──────────────╲
   ╱   Unit Tests   ╲  ← Nhiều nhất, nhanh nhất
  ╱──────────────────╲

📖 Unit Tests

Test isolated logic, mock dependencies

// scoring.service.spec.ts
describe('ScoringService', () => {
  let service: ScoringService;

  beforeEach(async () => {
    const module = await Test.createTestingModule({
      providers: [ScoringService],
    }).compile();

    service = module.get<ScoringService>(ScoringService);
  });

  describe('calculate', () => {
    it('should return 0 for incorrect answer', () => {
      expect(service.calculate(false, 0)).toBe(0);
    });

    it('should return max score for instant correct answer', () => {
      expect(service.calculate(true, 0)).toBe(1000);
    });

    it('should return proportional score based on time', () => {
      expect(service.calculate(true, 10000)).toBe(500);
    });
  });
});

📖 Integration Tests

Test with real database, mock external services

// quiz.controller.spec.ts
describe('QuizController (Integration)', () => {
  let app: INestApplication;
  let quizService: QuizService;

  beforeAll(async () => {
    const module = await Test.createTestingModule({
      imports: [AppModule],
    }).compile();

    app = module.createNestApplication();
    await app.init();
    quizService = module.get<QuizService>(QuizService);
  });

  afterAll(async () => {
    await app.close();
  });

  it('POST /quizzes - should create quiz', async () => {
    const response = await request(app.getHttpServer())
      .post('/quizzes')
      .set('Authorization', 'Bearer valid-token')
      .send({ title: 'Test Quiz', timePerQuestion: 30 })
      .expect(201);

    expect(response.body).toHaveProperty('id');
    expect(response.body.title).toBe('Test Quiz');
  });

  it('GET /quizzes - should return all quizzes', async () => {
    const response = await request(app.getHttpServer())
      .get('/quizzes')
      .set('Authorization', 'Bearer valid-token')
      .expect(200);

    expect(Array.isArray(response.body)).toBe(true);
  });
});

📖 E2E WebSocket Tests

// game.e2e-spec.ts
import { io, Socket } from 'socket.io-client';

describe('Game Flow (E2E)', () => {
  let hostSocket: Socket;
  let playerSocket: Socket;
  let app: INestApplication;

  beforeAll(async () => {
    const module = await Test.createTestingModule({
      imports: [AppModule],
    }).compile();

    app = module.createNestApplication();
    await app.init();
    await app.listen(3001);
  });

  beforeEach(() => {
    hostSocket = io('http://localhost:3001', { autoConnect: false });
    playerSocket = io('http://localhost:3001', { autoConnect: false });
  });

  afterEach(() => {
    hostSocket.disconnect();
    playerSocket.disconnect();
  });

  afterAll(async () => {
    await app.close();
  });

  it('should complete full game flow', (done) => {
    let pin: string;

    hostSocket.connect();
    
    // 1. Host creates room
    hostSocket.emit('createRoom', { quizId: 'test-quiz' }, (response) => {
      expect(response.success).toBe(true);
      pin = response.pin;

      // 2. Player joins
      playerSocket.connect();
      playerSocket.emit('joinRoom', { pin, nickname: 'TestPlayer' }, (res) => {
        expect(res.success).toBe(true);
      });
    });

    // 3. Player joined event
    hostSocket.on('playerJoined', (data) => {
      expect(data.newPlayer).toBe('TestPlayer');
      
      // 4. Host starts game
      hostSocket.emit('startGame', { quizId: 'test-quiz' });
    });

    // 5. Questions flow
    playerSocket.on('newQuestion', (data) => {
      expect(data.question).toBeDefined();
      
      // 6. Player answers
      playerSocket.emit('submitAnswer', { optionIndex: 0 });
    });

    // 7. Game over
    playerSocket.on('gameOver', (data) => {
      expect(data.leaderboard).toBeDefined();
      done();
    });
  });
});

---

2.3 Swagger Documentation

📖 Setup

// main.ts
import { SwaggerModule, DocumentBuilder } from '@nestjs/swagger';

async function bootstrap() {
  const app = await NestFactory.create(AppModule);

  const config = new DocumentBuilder()
    .setTitle('Quiz Realtime API')
    .setDescription('API documentation for Quiz Realtime application')
    .setVersion('1.0')
    .addBearerAuth()
    .build();

  const document = SwaggerModule.createDocument(app, config);
  SwaggerModule.setup('api-docs', app, document);

  await app.listen(3000);
}

📖 Decorating Controllers

import { ApiTags, ApiOperation, ApiResponse, ApiBearerAuth } from '@nestjs/swagger';

@ApiTags('quizzes')
@Controller('quizzes')
export class QuizController {
  
  @Post()
  @ApiBearerAuth()
  @ApiOperation({ summary: 'Create a new quiz' })
  @ApiResponse({ status: 201, description: 'Quiz created successfully' })
  @ApiResponse({ status: 401, description: 'Unauthorized' })
  create(@Body() dto: CreateQuizDto) {
    return this.quizService.create(dto);
  }
}

📖 Decorating DTOs

import { ApiProperty } from '@nestjs/swagger';

export class CreateQuizDto {
  @ApiProperty({
    example: 'JavaScript Basics',
    description: 'Title of the quiz',
  })
  @IsString()
  title: string;

  @ApiProperty({
    example: 30,
    description: 'Time limit per question in seconds',
    default: 30,
  })
  @IsNumber()
  timePerQuestion: number;
}

---

2.4 Graceful Shutdown

// main.ts
async function bootstrap() {
  const app = await NestFactory.create(AppModule);

  // Enable shutdown hooks
  app.enableShutdownHooks();

  await app.listen(3000);
}

// In Gateway
@WebSocketGateway()
export class GameGateway implements OnModuleDestroy {
  @WebSocketServer()
  server: Server;

  async onModuleDestroy() {
    // Notify all clients
    this.server.emit('serverShutdown', {
      message: 'Server is shutting down',
    });

    // Close all connections gracefully
    this.server.disconnectSockets(true);
    
    // Cleanup Redis
    // Save game states if needed
  }
}

---

2.5 Production Checklist

// Environment configuration
@Module({
  imports: [
    ConfigModule.forRoot({
      isGlobal: true,
      envFilePath: `.env.${process.env.NODE_ENV}`,
    }),
  ],
})
export class AppModule {}

// Docker production
// Dockerfile
FROM node:18-alpine AS builder
WORKDIR /app
COPY package*.json ./
RUN npm ci
COPY . .
RUN npm run build

FROM node:18-alpine AS production
WORKDIR /app
COPY --from=builder /app/dist ./dist
COPY --from=builder /app/node_modules ./node_modules
EXPOSE 3000
CMD ["node", "dist/main"]

---

3. STEP BY STEP TRIỂN KHAI

Bước 1: Setup Global Exception Filters

// src/common/filters/all-exceptions.filter.ts
// (Code như trên)

// src/common/filters/ws-exception.filter.ts
// (Code như trên)

// main.ts
app.useGlobalFilters(new AllExceptionsFilter());

Bước 2: Viết Unit Tests

# Run tests
npm run test

# Run with coverage
npm run test:cov

# Watch mode
npm run test:watch

// Tạo tests cho các services
// src/game/scoring.service.spec.ts
// src/game/room.service.spec.ts
// src/auth/auth.service.spec.ts

Bước 3: Setup Swagger

npm install @nestjs/swagger swagger-ui-express

Truy cập: http://localhost:3000/api-docs

Bước 4: Viết E2E Tests

npm run test:e2e

Bước 5: Docker Production Build

docker build -t quiz-realtime .
docker run -p 3000:3000 quiz-realtime

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4. VERIFY CHECKLIST

📋 Câu hỏi LÝ THUYẾT

#	Câu hỏi	Đáp án mong đợi
1	Unit test khác Integration test như thế nào?	Unit = isolated, mock deps; Integration = real deps
2	ExceptionFilter dùng để làm gì?	Catch và transform exceptions thành responses
3	WsException khác HttpException thế nào?	WsException cho WebSocket, emit event thay vì HTTP response
4	Swagger giúp gì trong development?	API documentation, testing interface
5	Graceful shutdown quan trọng vì sao?	Không mất data, cleanup resources
6	Test coverage nên đạt bao nhiêu %?	80%+ cho critical services

📋 Câu hỏi THỰC HÀNH

#	Kiểm tra	Cách verify
1	Unit tests pass?	npm run test → All green
2	Test coverage đủ?	npm run test:cov → >80%
3	Swagger hoạt động?	http://localhost:3000/api-docs
4	Error handling đúng?	Throw error → Client nhận formatted response
5	E2E test pass?	npm run test:e2e → Full flow works
6	Docker build thành công?	docker build → Image created

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5. 🏆 FINAL ASSESSMENT

5.1 Knowledge Verification

Bạn có thể giải thích được:

Topic	Câu hỏi kiểm tra
NestJS Core	Module, Provider, DI hoạt động ra sao?
TypeORM	Entity, Relations, Migration là gì?
Authentication	JWT flow, Guards, Strategies?
WebSocket	Gateway, Rooms, Event broadcasting?
Redis	Data structures, Pub/Sub, Adapter?
Game Engine	State machine, Scoring, Race condition?
Testing	Unit vs Integration vs E2E?

5.2 Skills Verification

Skill	Cách demonstrate
Setup project	nest new → Docker Compose → Running
CRUD API	Swagger shows all endpoints
Authentication	Login → JWT → Protected routes
Real-time	Create room → Join → Chat works
Game logic	Play full game from start to end
Testing	npm test → All pass

5.3 Presentation Checklist

Có thể demo cho người khác:

• Tạo quiz mới qua Swagger
• Host tạo phòng, lấy PIN
• Players join bằng PIN
• Chơi 1 game hoàn chỉnh
• Xem leaderboard real-time
• Giải thích architecture diagram
• Giải thích data flow

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6. MỞ RỘNG - NEXT STEPS

6.1 Features có thể thêm

Feature	Độ phức tạp
Upload ảnh cho questions	⭐⭐
Multiple game modes	⭐⭐⭐
Analytics dashboard	⭐⭐⭐
Mobile app (React Native)	⭐⭐⭐⭐

6.2 Infrastructure upgrades

Upgrade	Khi nào cần
Redis Cluster	> 1000 concurrent rooms
Kubernetes	Need auto-scaling
Message Queue (BullMQ)	Heavy background jobs
CDN	Serve static assets

6.3 Learning continuation

Topic	Resources
Microservices	NestJS microservices docs
GraphQL	NestJS GraphQL module
gRPC	High-performance inter-service
Event Sourcing	Complex game state

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📅 Timeline Tuần 6

Ngày	Hoạt động	Thời gian
Ngày 1-2	Exception filters + Unit tests	3-4 giờ
Ngày 3-4	Integration + E2E tests	3-4 giờ
Ngày 5	Swagger + Documentation	2-3 giờ
Ngày 6	Docker + Deployment prep	2-3 giờ
Ngày 7	🎉 Final demo + Review	2 giờ

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🎓 TỔNG KẾT KHÓA HỌC

Tuần 1: NestJS Fundamentals    → Hiểu Module, DI, Controllers
Tuần 2: TypeORM + Auth         → Database, JWT, Guards
Tuần 3: WebSocket Basics       → Gateway, Rooms, Events
Tuần 4: Redis Integration      → Data structures, Pub/Sub
Tuần 5: Game Engine            → State machine, Scoring
Tuần 6: Polish + Testing       → Production-ready app

💡 Lời kết: Bạn đã xây dựng được một ứng dụng real-time hoàn chỉnh với NestJS. Kiến thức này có thể áp dụng cho: chat apps, live dashboards, collaborative tools, gaming platforms, và nhiều hơn nữa!

Chúc mừng bạn đã hoàn thành khóa học! 🎉