feature: 쿠폰 조회 로직 및 관련 통합테스트 작성

Author: yeonjiyeon

apps/commerce-api/src/main/java/com/loopers/domain/coupon/CouponRepository.java

@@ -0,0 +1,10 @@
+package com.loopers.domain.coupon;
+
+import java.util.Optional;
+
+public interface CouponRepository {
+
+  Coupon save(Coupon coupon);
+
+  Optional<Coupon> findById(Long id);
+}

apps/commerce-api/src/main/java/com/loopers/domain/coupon/CouponService.java

@@ -0,0 +1,19 @@
+package com.loopers.domain.coupon;
+
+import com.loopers.support.error.CoreException;
+import com.loopers.support.error.ErrorType;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+
+@RequiredArgsConstructor
+@Component
+public class CouponService {
+
+  private final CouponRepository couponRepository;
+
+
+  public Coupon getCoupon(Long id) {
+    return couponRepository.findById(id)
+        .orElseThrow(() -> new CoreException(ErrorType.NOT_FOUND, "쿠폰을 찾을 수 없습니다."));
+  }
+}

apps/commerce-api/src/main/java/com/loopers/infrastructure/coupon/CouponJpaRepository.java

@@ -0,0 +1,8 @@
+package com.loopers.infrastructure.coupon;
+
+import com.loopers.domain.coupon.Coupon;
+import org.springframework.data.jpa.repository.JpaRepository;
+
+public interface CouponJpaRepository extends JpaRepository<Coupon, Long> {
+
+}

apps/commerce-api/src/main/java/com/loopers/infrastructure/coupon/CouponRepositoryImpl.java

@@ -0,0 +1,24 @@
+package com.loopers.infrastructure.coupon;
+
+import com.loopers.domain.coupon.Coupon;
+import com.loopers.domain.coupon.CouponRepository;
+import java.util.Optional;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Component;
+
+@RequiredArgsConstructor
+@Component
+public class CouponRepositoryImpl implements CouponRepository {
+
+  private final CouponJpaRepository couponJpaRepository;
+
+  @Override
+  public Coupon save(Coupon coupon) {
+    return couponJpaRepository.save(coupon);
+  }
+
+  @Override
+  public Optional<Coupon> findById(Long id) {
+    return couponJpaRepository.findById(id);
+  }
+}

apps/commerce-api/src/test/java/com/loopers/domain/coupon/CouponServiceIntegrationTest.java

@@ -0,0 +1,67 @@
+package com.loopers.domain.coupon;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.jupiter.api.Assertions.*;
+
+import com.loopers.domain.user.User;
+import com.loopers.domain.user.User.Gender;
+import com.loopers.domain.user.UserRepository;
+import com.loopers.utils.DatabaseCleanUp;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.test.context.bean.override.mockito.MockitoSpyBean;
+import org.springframework.transaction.annotation.Transactional;
+
+@SpringBootTest
+@Transactional
+class CouponServiceIntegrationTest {
+
+  @Autowired
+  CouponService couponService;
+
+  @MockitoSpyBean
+  CouponRepository couponRepository;
+
+  @MockitoSpyBean
+  UserRepository userRepository;
+
+  @Autowired
+  private DatabaseCleanUp databaseCleanUp;
+
+  @AfterEach
+  void tearDown() {
+    databaseCleanUp.truncateAllTables();
+  }
+
+  @DisplayName("쿠폰 조회 시,")
+  @Nested
+  class GetCoupon {
+
+    @DisplayName("존재하는 쿠폰이면 조회된다.")
+    @Test
+    void getCoupon_success_whenExists() {
+      // arrange
+      User user = userRepository.save(new User("user1", "a@email.com", "2025-11-11", Gender.FEMALE));
+      Coupon coupon = couponRepository.save(
+          new Coupon(user.getId(), CouponType.FIXED_AMOUNT, 10)
+      );
+
+      // act
+      Coupon found = couponService.getCoupon(coupon.getId());
+
+      // assert
+      assertThat(found).isNotNull();
+      assertThat(found.getId()).isEqualTo(coupon.getId());
+    }
+
+    @DisplayName("존재하지 않는 쿠폰이면 예외가 발생한다.")
+    @Test
+    void getCoupon_fail_whenNotFound() {
+      assertThrows(RuntimeException.class, () -> couponService.getCoupon(999L));
+    }
+  }
+}