test: add database compatibility tests

- Add comprehensive tests for formatBoolean() function
- Test PostgreSQL vs SQLite boolean handling
- Test date formatting and manipulation functions
- Verify insertAndGetId handles both database result formats

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

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

backend/src/__tests__/dbCompat.test.js

@@ -0,0 +1,83 @@
+const { formatBoolean, isPostgreSQL, addDays, formatDateForDB, insertAndGetId } = require('../utils/dbCompat');
+
+describe('Database Compatibility', () => {
+  // Save original env
+  const originalEnv = process.env.DATABASE_CLIENT;
+  
+  afterEach(() => {
+    // Restore original env after each test
+    if (originalEnv) {
+      process.env.DATABASE_CLIENT = originalEnv;
+    } else {
+      delete process.env.DATABASE_CLIENT;
+    }
+  });
+
+  describe('formatBoolean', () => {
+    test('should format boolean values correctly', () => {
+      // Mock for SQLite
+      process.env.DATABASE_CLIENT = 'sqlite3';
+      expect(formatBoolean(true)).toBe(1);
+      expect(formatBoolean(false)).toBe(0);
+      
+      // Mock for PostgreSQL
+      process.env.DATABASE_CLIENT = 'pg';
+      expect(formatBoolean(true)).toBe(true);
+      expect(formatBoolean(false)).toBe(false);
+      
+      // Default (no env var) should be SQLite
+      delete process.env.DATABASE_CLIENT;
+      expect(formatBoolean(true)).toBe(1);
+      expect(formatBoolean(false)).toBe(0);
+    });
+  });
+
+  describe('isPostgreSQL', () => {
+    test('should detect PostgreSQL correctly', () => {
+      process.env.DATABASE_CLIENT = 'pg';
+      expect(isPostgreSQL()).toBe(true);
+      
+      process.env.DATABASE_CLIENT = 'sqlite3';
+      expect(isPostgreSQL()).toBe(false);
+      
+      delete process.env.DATABASE_CLIENT;
+      expect(isPostgreSQL()).toBe(false); // Default to SQLite
+    });
+  });
+
+  describe('formatDateForDB', () => {
+    test('should format dates as ISO strings', () => {
+      const date = new Date('2024-01-15T10:30:00Z');
+      expect(formatDateForDB(date)).toBe('2024-01-15T10:30:00.000Z');
+    });
+  });
+
+  describe('addDays', () => {
+    test('should add days correctly', () => {
+      const date = new Date('2024-01-15');
+      const result = addDays(date, 30);
+      expect(result.toISOString().split('T')[0]).toBe('2024-02-14');
+      
+      const negativeResult = addDays(date, -7);
+      expect(negativeResult.toISOString().split('T')[0]).toBe('2024-01-08');
+    });
+  });
+
+  describe('insertAndGetId', () => {
+    test('should handle PostgreSQL result format', async () => {
+      const mockQuery = {
+        returning: jest.fn().mockResolvedValue([{ id: 123 }])
+      };
+      const result = await insertAndGetId(mockQuery);
+      expect(result).toBe(123);
+    });
+
+    test('should handle SQLite result format', async () => {
+      const mockQuery = {
+        returning: jest.fn().mockResolvedValue([456])
+      };
+      const result = await insertAndGetId(mockQuery);
+      expect(result).toBe(456);
+    });
+  });
+});