عرض عملي: ربط Shop Core يدويًا ثم باستخدام Spring

خطوة بخطوة

1. Show main building PricingService, PaymentProvider, and OrderService with new.
2. Annotate the services with @Service and keep constructor parameters.
3. Delete the new calls from main; run the Boot app.
4. Planned mistake: put @Autowired on a field and write a unit test with new OrderService(...); the field is null and the test fails. Fix: switch to constructor injection.
5. Show that the unit test now passes a fake PaymentProvider.