add tests for config/config and nodeEnv

src/__tests__/config.test.ts

@@ -0,0 +1,13 @@
+import { config } from '../config/config.js';
+
+describe('Configuration', () => {
+  test('should load configuration successfully', () => {
+    expect(config).toBeDefined();
+    expect(config.mongodbUri).toBeDefined();
+    expect(config.nodeEnv).toBeDefined();
+  });
+
+  test('should have valid environment', () => {
+    expect(['development', 'production', 'test']).toContain(config.nodeEnv);
+  });
+});