Logging Testing — Testing Log Output and Logging Behavior

// Test log capture utility
class TestLogCapture {
  constructor() {
    this.entries = [];
    this.originalTransport = null;
  }

  attach(logger) {
    const transport = new winston.transports.Stream({
      stream: new require('stream').Writable({
        write: (chunk, encoding, callback) => {
          this.entries.push(JSON.parse(chunk.toString()));
          callback();
        }
      })
    });

    logger.add(transport);
    this.originalTransport = transport;
  }

  detach(logger) {
    if (this.originalTransport) {
      logger.remove(this.originalTransport);
    }
  }

  getEntries() { return this.entries; }
  getErrors() { return this.entries.filter(e => e.level === 'ERROR'); }
  contains(message) { return this.entries.some(e => e.message.includes(message)); }
  findByCorrelationId(id) { return this.entries.filter(e => e.correlationId === id); }
  findByType(type) { return this.entries.filter(e => e.type === type); }
  clear() { this.entries = []; }
}

// Test example
describe('ScanController logging', () => {
  let capture;
  let logger;

  beforeEach(() => {
    capture = new TestLogCapture();
    capture.attach(logger);
  });

  afterEach(() => {
    capture.detach(logger);
  });

  it('should log scan initiation', async () => {
    await request(app)
      .post('/api/scans')
      .send({ fileId: 'test-123' })
      .expect(201);

    const logEntry = capture.findByType('scan.initiated');
    expect(logEntry).toHaveLength(1);
    expect(logEntry[0].message).toContain('test-123');
    expect(logEntry[0].userId).toBeDefined();
    expect(logEntry[0].correlationId).toBeDefined();
  });

  it('should log errors with stack traces', async () => {
    await request(app)
      .post('/api/scans')
      .send({})
      .expect(400);

    const errors = capture.getErrors();
    expect(errors.length).toBeGreaterThan(0);
    expect(errors[0].stack).toBeDefined();
  });

  it('should not log sensitive data', async () => {
    await request(app).post('/auth/login')
      .send({ email: 'test@example.com', password: 'supersecret' });

    const logs = capture.getEntries();
    const logString = JSON.stringify(logs);
    expect(logString).not.toContain('supersecret');
  });
});