test: 동시성 테스트 코드 작성

src/main/java/com/rentify/rentify_api/coupon/entity/Coupon.java

@@ -8,17 +8,14 @@
 import jakarta.persistence.GenerationType;
 import jakarta.persistence.Id;
 import jakarta.persistence.Table;
-import jakarta.persistence.Version;
 import java.time.LocalDateTime;
 import lombok.AccessLevel;
 import lombok.AllArgsConstructor;
 import lombok.Builder;
 import lombok.Getter;
 import lombok.NoArgsConstructor;
 import org.hibernate.annotations.CreationTimestamp;
-import org.hibernate.annotations.JdbcTypeCode;
 import org.hibernate.annotations.UpdateTimestamp;
-import org.hibernate.type.SqlTypes;
 
 @Entity
 @Table(name = "coupons")
@@ -36,11 +33,11 @@ public class Coupon {
     @Column(name = "coupon_name", nullable = false, length = 100)
     private String couponName;
 
-    @Column(name = "description", length = 255)
+    @Column(name = "description")
     private String description;
 
     @Enumerated(EnumType.STRING)
-    @Column(name = "discount_type", nullable = false, columnDefinition = "coupon_discount_type")
+    @Column(name = "discount_type", nullable = false)
     private CouponDiscountType discountType;
 
     @Column(name = "discount_value", nullable = false)
@@ -68,7 +65,7 @@ public class Coupon {
     private LocalDateTime validUntil;
 
     @Enumerated(EnumType.STRING)
-    @Column(name = "status", nullable = false, columnDefinition = "coupon_status")
+    @Column(name = "status", nullable = false)
     private CouponStatus status;
 
     @CreationTimestamp

src/main/java/com/rentify/rentify_api/coupon/entity/UserCoupon.java

@@ -53,7 +53,7 @@ public class UserCoupon {
     private LocalDateTime usedAt;
 
     @Enumerated(EnumType.STRING)
-    @Column(name = "status", nullable = false, columnDefinition = "user_coupon_status")
+    @Column(name = "status", nullable = false)
     private UserCouponStatus status;
 
     @Version

src/main/java/com/rentify/rentify_api/post/entity/Post.java

@@ -18,7 +18,6 @@
 import jakarta.persistence.JoinColumn;
 import jakarta.persistence.ManyToOne;
 import jakarta.persistence.OneToMany;
-import jakarta.persistence.OneToOne;
 import jakarta.persistence.Table;
 import java.time.LocalDateTime;
 import java.util.ArrayList;
@@ -49,7 +48,7 @@ public class Post {
     @JoinColumn(name = "user_id", nullable = false)
     private User user;
 
-    @OneToOne(fetch = FetchType.LAZY)
+    @ManyToOne(fetch = FetchType.LAZY)
     @JoinColumn(name = "category_id", nullable = false)
     private Category category;
 

src/main/java/com/rentify/rentify_api/rental/service/RentalService.java

@@ -41,7 +41,7 @@ public RentalResponse createRental(Long userId, RentalRequest request) {
                 .orElseThrow(UserNotFoundException::new);
 
         // 게시글 조회
-        Post post = postRepository.findById(request.getPostId())
+        Post post = postRepository.findByIdWithPessimisticLock(request.getPostId())
             .orElseThrow(() -> new NotFoundException("게시글을 찾을 수 없습니다."));
 
         // 본인의 게시글 여부 확인

src/test/java/com/rentify/rentify_api/coupon/service/CouponConcurrencyTest.java

@@ -0,0 +1,189 @@
+package com.rentify.rentify_api.coupon.service;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import com.rentify.rentify_api.common.filter.JwtAuthenticationFilter;
+import com.rentify.rentify_api.common.jwt.JwtTokenProvider;
+import com.rentify.rentify_api.coupon.entity.Coupon;
+import com.rentify.rentify_api.coupon.entity.CouponDiscountType;
+import com.rentify.rentify_api.coupon.entity.CouponStatus;
+import com.rentify.rentify_api.coupon.repository.CouponRepository;
+import com.rentify.rentify_api.coupon.repository.UserCouponRepository;
+import com.rentify.rentify_api.user.entity.User;
+import com.rentify.rentify_api.user.repository.UserRepository;
+import java.time.LocalDateTime;
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.test.context.bean.override.mockito.MockitoBean;
+
+@SpringBootTest
+class CouponConcurrencyTest {
+
+    @Autowired
+    CouponService couponService;
+
+    @Autowired
+    CouponRepository couponRepository;
+
+    @Autowired
+    UserCouponRepository userCouponRepository;
+
+    @Autowired
+    UserRepository userRepository;
+
+    @MockitoBean
+    JwtTokenProvider jwtTokenProvider;
+
+    @MockitoBean
+    JavaMailSender mailSender;
+
+    @MockitoBean
+    JwtAuthenticationFilter jwtAuthenticationFilter;
+
+    private Coupon coupon;
+    private List<User> users;
+
+    @BeforeEach
+    void setUp() {
+        coupon = couponRepository.save(Coupon.builder()
+            .couponName("선착순 테스트 쿠폰")
+            .description("동시성 테스트용 쿠폰")
+            .discountValue(1000)
+            .discountType(CouponDiscountType.FIXED)
+            .maxDiscountAmount(1000)
+            .minOrderAmount(5000)
+            .totalQuantity((short) 10)
+            .issuedQuantity((short) 0)
+            .perUserLimit((short) 1)
+            .validFrom(LocalDateTime.now().minusDays(1))
+            .validUntil(LocalDateTime.now().plusDays(30))
+            .status(CouponStatus.ACTIVE)
+            .build());
+
+        users = new ArrayList<>();
+        for (int i = 0; i < 20; i++) {
+            users.add(userRepository.save(User.builder()
+                .name("유저" + i)
+                .email("coupon-test-" + i + "@test.com")
+                .password("password")
+                .build())
+            );
+        }
+    }
+
+    @AfterEach
+    void tearDown() {
+        userCouponRepository.deleteAll();
+        couponRepository.deleteAll();
+        userRepository.deleteAll();
+    }
+
+    @Test
+    @DisplayName("수량 10개 쿠폰에 20명이 동시 요청 시 정확히 10명만 발급 성공")
+    void concurrency_coupon_issue_should_limit_to_total_quantity() throws InterruptedException {
+        // given
+        int threadCount = 20;
+        ExecutorService executorService = Executors.newFixedThreadPool(threadCount);
+        CountDownLatch readyLatch = new CountDownLatch(threadCount);
+        CountDownLatch startLatch = new CountDownLatch(1);
+        CountDownLatch doneLatch = new CountDownLatch(threadCount);
+
+        AtomicInteger successCount = new AtomicInteger();
+        AtomicInteger failCount = new AtomicInteger();
+
+        // when
+        for (int i = 0; i < threadCount; i++) {
+            final Long userId = users.get(i).getId();
+            executorService.execute(() -> {
+                readyLatch.countDown();
+                try {
+                    startLatch.await();
+                    couponService.issueCoupon(userId, coupon.getId());
+                    successCount.incrementAndGet();
+                } catch (Exception e) {
+                    failCount.incrementAndGet();
+                } finally {
+                    doneLatch.countDown();
+                }
+            });
+        }
+
+        readyLatch.await();
+        startLatch.countDown();
+        doneLatch.await();
+
+        // then
+        long issuedCount = userCouponRepository.count();
+        Coupon updatedCoupon = couponRepository.findById(coupon.getId()).orElseThrow();
+
+        System.out.println("성공: " + successCount.get());
+        System.out.println("실패: " + failCount.get());
+        System.out.println("실제 발급 수: " + issuedCount);
+        System.out.println("쿠폰 issuedQuantity: " + updatedCoupon.getIssuedQuantity());
+
+        assertThat(successCount.get()).isEqualTo(10);
+        assertThat(failCount.get()).isEqualTo(10);
+        assertThat(issuedCount).isEqualTo(10);
+        assertThat(updatedCoupon.getIssuedQuantity()).isEqualTo((short) 10);
+        assertThat(updatedCoupon.getStatus()).isEqualTo(CouponStatus.INACTIVE);
+
+        executorService.shutdown();
+    }
+
+    @Test
+    @DisplayName("같은 유저가 동시에 여러 번 요청해도 perUserLimit 만큼만 발급됨")
+    void concurrency_same_user_should_respect_per_user_limit() throws InterruptedException {
+        // given
+        int threadCount = 10;
+        ExecutorService executorService = Executors.newFixedThreadPool(10);
+        CountDownLatch readyLatch = new CountDownLatch(threadCount);
+        CountDownLatch startLatch = new CountDownLatch(1);
+        CountDownLatch doneLatch = new CountDownLatch(threadCount);
+
+        Long userId = users.get(0).getId();
+        AtomicInteger successCount = new AtomicInteger();
+        AtomicInteger failCount = new AtomicInteger();
+
+        for (int i = 0; i < threadCount; i++) {
+            executorService.execute(() -> {
+                readyLatch.countDown();
+                try {
+                    startLatch.await();
+                    couponService.issueCoupon(userId, coupon.getId());
+                    successCount.incrementAndGet();
+                } catch (Exception e) {
+                    failCount.incrementAndGet();
+                } finally {
+                    doneLatch.countDown();
+                }
+            });
+        }
+
+        readyLatch.await();
+        startLatch.countDown();
+        doneLatch.await();
+
+        long userCouponCount = userCouponRepository.countByUserIdAndCouponId(userId,
+            coupon.getId());
+
+        System.out.println("같은 유저 - 성공: " + successCount.get());
+        System.out.println("같은 유저 - 실패: " + failCount.get());
+        System.out.println("같은 유저 발급 수: " + userCouponCount);
+
+        assertThat(successCount.get()).isEqualTo(1);
+        assertThat(userCouponCount).isEqualTo(1);
+
+        executorService.shutdown();
+    }
+}