عرض عملي: بناء Controller بأسلوب الاختبار أولًا باستخدام @WebMvcTest

خطوة بخطوة

1. Write a failing test for the success case; mock the service; assert status and JSON fields.
2. Make it pass (the controller from JNR-013).
3. Add a validation test: POST /products with a blank name returns 400 and a field error.
4. Planned mistake: assert only status().isOk(), and a bug in the JSON passes. Fix: add jsonPath assertions.
5. Add the not-found test and check the Problem Details body.