[테스트] Jest 테스트 세팅 추가

[Copilot]

This PR adds a comprehensive Jest testing setup to the ClipBE-Express project, enabling developers to write and run tests for the Express.js application with full ES modules support.

What's Added

Jest Configuration

• Jest with ES modules support using NODE_OPTIONS='--experimental-vm-modules'
• Clean jest.config.js configuration optimized for Node.js environment
• Proper test file patterns and coverage collection settings

Test Scripts

Added three new npm scripts for different testing scenarios:

npm test              # Run all tests once
npm run test:watch    # Run tests in watch mode for development
npm run test:coverage # Generate coverage reports

Test Structure

Created organized test directory structure:

__tests__/
├── utils/
│   ├── responseFormatter.test.js
│   └── errors.test.js
└── apis/clip/service/
    └── getAllClips.test.js

Example Tests

• Utility function tests: Comprehensive tests for responseFormatter and CustomError classes with 100% coverage
• Service layer tests: Demonstrates mocking capabilities with the getAllClips service, showing how to mock repository dependencies
• 14 tests total covering various scenarios including edge cases

Development Environment Integration

• Updated .gitignore to exclude test coverage reports
• Enhanced ESLint configuration to support Jest globals in test files
• All tests pass linting with existing code style rules

Testing Example

The setup enables testing patterns like this:

// Testing utilities
import { createSuccessResponse } from '../../src/utils/responseFormatter.js';

test('should create success response with data', () => {
  const result = createSuccessResponse({ message: 'Test' });
  expect(result.status).toBe('SUCCESS');
  expect(result.data.message).toBe('Test');
});

// Testing services with mocks
jest.unstable_mockModule('repository/findAllClips.js', () => ({
  findAllClips: jest.fn()
}));

test('should format clips data correctly', async () => {
  findAllClips.mockResolvedValue(mockData);
  const result = await getAllClips();
  expect(result.status).toBe('SUCCESS');
});

Test Results

✅ All 14 tests passing
✅ 100% coverage on utility functions
✅ Proper mocking capabilities demonstrated
✅ ES modules compatibility confirmed

Fixes #17.

Warning

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