add: comprehensive TDD test infrastructure

- Add Vitest + jsdom testing framework
- Create unit tests for engine.js and generator.js
- Add integration tests for end-to-end workflows
- Include test utilities and setup helpers
- Document testing approach in TESTING.md
- Document all dependencies in DEPENDS.md
- Add Makefile with test targets and dev workflow

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

TESTING.md

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+# Timeline SVG - Test Infrastructure
+
+This document describes the test-driven development (TDD) infrastructure for the Timeline SVG Generator project.
+
+## Test Framework Setup
+
+The project uses **Vitest** with **jsdom** for testing browser-based JavaScript code.
+
+### Dependencies
+
+```json
+{
+  "@vitest/ui": "^2.1.0",
+  "@vitest/coverage-v8": "^2.1.0",
+  "jsdom": "^25.0.0",
+  "vitest": "^2.1.0"
+}
+```
+
+### Installation
+
+```bash
+npm install
+```
+
+## Running Tests
+
+```bash
+# Run all tests once
+npm test
+
+# Run tests in watch mode (for TDD)
+npm run test:watch
+
+# Run with coverage report
+npm run test:coverage
+
+# Open test UI (browser-based test runner)
+npm run test:ui
+```
+
+## Test Structure
+
+### Unit Tests
+
+- **`test/engine.test.js`** - Tests for timeline data processing
+  - CSV parsing and validation
+  - Date parsing (multiple formats)
+  - Project configuration loading
+  - DOM integration
+
+- **`test/generator.test.js`** - Tests for SVG generation
+  - SVG template processing
+  - Month grid generation
+  - Lane and item positioning
+  - XML escaping
+
+### Integration Tests
+
+- **`test/integration.test.js`** - End-to-end workflow tests
+  - Complete timeline generation pipeline
+  - File upload simulation
+  - DOM event handling
+  - Export functionality
+
+### Test Utilities
+
+- **`test/setup.js`** - Global test setup and mocks
+- **`test/testHelpers.js`** - Common test data and utilities
+
+## TDD Workflow
+
+### 1. Red Phase - Write Failing Test
+
+```bash
+# Start test watcher
+npm run test:watch
+
+# Create test for new feature
+touch test/newFeature.test.js
+```
+
+Example test:
+```javascript
+describe('New Feature', () => {
+  it('should do something specific', () => {
+    const result = myNewFunction('input')
+    expect(result).toBe('expected output')
+  })
+})
+```
+
+### 2. Green Phase - Make Test Pass
+
+Implement minimal code to make the test pass:
+
+```javascript
+// In the appropriate source file
+function myNewFunction(input) {
+  return 'expected output'  // Minimal implementation
+}
+```
+
+### 3. Refactor Phase - Improve Code
+
+```bash
+# Ensure tests still pass after refactoring
+npm test
+```
+
+## Key Testing Patterns
+
+### Mocking Browser APIs
+
+```javascript
+// In test/setup.js
+global.fetch = vi.fn()
+global.Papa = { parse: vi.fn() }
+
+// In tests
+mockFetch(sampleData)
+```
+
+### DOM Testing
+
+```javascript
+// Setup DOM elements
+setupBasicDOM()
+
+// Test DOM manipulation
+await timelineEngine.loadProjectConfigObject(config)
+expectElementToHaveText('#projectName', 'Test Project')
+```
+
+### Testing Vanilla JS Modules
+
+Since the project uses global objects, tests load modules by evaluating the source:
+
+```javascript
+const fs = await import('fs/promises')
+const engineCode = await fs.readFile('./engine.js', 'utf-8')
+eval(engineCode)
+const timelineEngine = global.window.timelineEngine
+```
+
+## Coverage Goals
+
+- **Statements**: >90%
+- **Branches**: >85%
+- **Functions**: >90%
+- **Lines**: >90%
+
+View detailed coverage:
+```bash
+npm run test:coverage
+open coverage/index.html
+```
+
+## Common Test Scenarios
+
+### Testing Date Parsing
+
+```javascript
+it('should parse various date formats', () => {
+  expect(parseDate('2025-12-15')).toEqual(new Date(2025, 11, 15))
+  expect(parseDate('15.12.2025')).toEqual(new Date(2025, 11, 15))
+  expect(parseDate('invalid')).toBeNull()
+})
+```
+
+### Testing SVG Generation
+
+```javascript
+it('should generate valid SVG with timeline items', () => {
+  const result = timelineGenerator.generate(items, config, template)
+  expect(result).toContain('<svg xmlns="http://www.w3.org/2000/svg">')
+  expect(result).toContain('Task Title')
+})
+```
+
+### Testing Error Handling
+
+```javascript
+it('should handle missing configuration gracefully', () => {
+  const consoleSpy = vi.spyOn(console, 'error').mockImplementation(() => {})
+  timelineEngine.processCsv('data', null)
+  expect(consoleSpy).toHaveBeenCalledWith('No config or fieldMapping found.')
+})
+```
+
+## Debugging Tests
+
+### Using Test UI
+
+```bash
+npm run test:ui
+```
+
+Opens browser interface with:
+- Test results visualization
+- Coverage reports
+- Test file exploration
+- Real-time test watching
+
+### Console Debugging
+
+```javascript
+it('should debug test data', () => {
+  console.log('Debug data:', testData)
+  // Test continues...
+})
+```
+
+## Adding New Tests
+
+1. **Create test file** in `test/` directory
+2. **Import helpers** from `test/testHelpers.js`
+3. **Follow naming convention**: `*.test.js`
+4. **Group related tests** with `describe()` blocks
+5. **Use descriptive test names** with `it('should ...')`
+
+## CI Integration
+
+Tests can be easily integrated into CI pipelines:
+
+```yaml
+# GitHub Actions example
+- name: Run tests
+  run: npm test
+
+- name: Upload coverage
+  run: npm run test:coverage
+```
+
+## Best Practices
+
+1. **Test behavior, not implementation**
+2. **Use descriptive test names**
+3. **Keep tests focused and small**
+4. **Mock external dependencies**
+5. **Test both success and error cases**
+6. **Maintain test data helpers**
+7. **Run tests frequently during development**
+
+This test infrastructure enables confident refactoring and feature development while maintaining code quality and preventing regressions.