refactor: replace @DirtiesContext with shared containers and @Transactional rollback

backend/CLAUDE.md

@@ -114,23 +114,21 @@ class FooServiceTest {
 ```
 
 ### Integration Tests (`*IntegrationTest.java`)
+
+All integration tests extend `AbstractIntegrationTest`, which provides:
+- **Shared containers** — `SharedContainers` starts a single MySQL and Mailpit container per JVM (singleton pattern), shared by all test classes
+- **`@Transactional` rollback** — each test runs in a transaction that rolls back automatically, restoring the DataInitializer-seeded state without needing `@DirtiesContext`
+- **Common annotations** — `@SpringBootTest`, `@AutoConfigureMockMvc`, `@ActiveProfiles("dev")`, `@Tag("integration")`
+
 ```java
-@SpringBootTest
-@Testcontainers
-@AutoConfigureMockMvc
 @DisplayName("Integration tests for Foo API endpoints")
-@Tag("integration")
-@ActiveProfiles(value = "dev")
-public class FooIntegrationTest {
+public class FooIntegrationTest extends AbstractIntegrationTest {
     @Autowired MockMvc mockMvc;
     @Autowired JsonMapper jsonMapper;
 
     @Value("${api.endpoint.base-url}")
     String baseUrl;
 
-    @Container @ServiceConnection
-    static MySQLContainer<?> mysql = new MySQLContainer<>(DockerImageName.parse("mysql:8.0"));
-
     String adminToken;
     String studentToken;
 
@@ -153,4 +151,4 @@ public class FooIntegrationTest {
 }
 ```
 
-Integration tests use Testcontainers (MySQL 8.0), seed data from `DataInitializer`, and authenticate via HTTP Basic to get JWT tokens for subsequent requests. Tests verify both the `flag` and `code` fields in the `Result` response. Use `@DirtiesContext` on tests that modify state and could affect other tests.
+Integration tests use Testcontainers (MySQL 8.0), seed data from `DataInitializer`, and authenticate via HTTP Basic to get JWT tokens for subsequent requests. Tests verify both the `flag` and `code` fields in the `Result` response. Do **not** use `@DirtiesContext` — the `@Transactional` rollback on the base class handles database reset automatically.

backend/src/test/java/team/projectpulse/AbstractIntegrationTest.java

@@ -0,0 +1,40 @@
+package team.projectpulse;
+
+import org.junit.jupiter.api.Tag;
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
+import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
+import org.springframework.test.context.ActiveProfiles;
+import org.springframework.test.context.DynamicPropertyRegistry;
+import org.springframework.test.context.DynamicPropertySource;
+import org.springframework.transaction.annotation.Transactional;
+import org.testcontainers.containers.MySQLContainer;
+
+/**
+ * Base class for all integration tests. Provides:
+ * <ul>
+ *   <li>Shared MySQL and Mailpit containers via {@link SharedContainers} (started once per JVM)</li>
+ *   <li>{@code @Transactional} rollback after each test — restores DataInitializer-seeded state
+ *       without the cost of {@code @DirtiesContext} (which would recreate the entire Spring context)</li>
+ *   <li>Common annotations: {@code @SpringBootTest}, {@code @AutoConfigureMockMvc},
+ *       {@code @ActiveProfiles("dev")}, {@code @Tag("integration")}</li>
+ * </ul>
+ */
+@SpringBootTest
+@AutoConfigureMockMvc
+@ActiveProfiles("dev")
+@Tag("integration")
+@Transactional
+public abstract class AbstractIntegrationTest {
+
+    @ServiceConnection
+    static final MySQLContainer<?> mysql = SharedContainers.MYSQL;
+
+
+    @DynamicPropertySource
+    static void setProperties(DynamicPropertyRegistry registry) {
+        registry.add("spring.mail.host", SharedContainers.MAILPIT::getHost);
+        registry.add("spring.mail.port", () -> SharedContainers.MAILPIT.getMappedPort(1025));
+    }
+
+}

backend/src/test/java/team/projectpulse/ProjectPulseApplicationTests.java

@@ -1,21 +1,8 @@
 package team.projectpulse;
 
 import org.junit.jupiter.api.Test;
-import org.springframework.boot.test.context.SpringBootTest;
-import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
-import org.testcontainers.containers.MySQLContainer;
-import org.testcontainers.junit.jupiter.Container;
-import org.testcontainers.junit.jupiter.Testcontainers;
-import org.testcontainers.utility.DockerImageName;
 
-@SpringBootTest
-@Testcontainers
-class ProjectPulseApplicationTests {
-
-    @Container
-    @ServiceConnection
-    static MySQLContainer<?> mysql = new MySQLContainer<>(DockerImageName.parse("mysql:8.0"));
-
+class ProjectPulseApplicationTests extends AbstractIntegrationTest {
 
     @Test
     void contextLoads() {

backend/src/test/java/team/projectpulse/SharedContainers.java

@@ -0,0 +1,27 @@
+package team.projectpulse;
+
+import org.testcontainers.containers.GenericContainer;
+import org.testcontainers.containers.MySQLContainer;
+import org.testcontainers.utility.DockerImageName;
+
+/**
+ * Singleton containers shared by all integration tests. Started once per JVM — avoids
+ * spinning up a new MySQL/Mailpit container per test class.
+ */
+public final class SharedContainers {
+
+    public static final MySQLContainer<?> MYSQL = new MySQLContainer<>(DockerImageName.parse("mysql:8.0"));
+
+    public static final GenericContainer<?> MAILPIT = new GenericContainer<>(DockerImageName.parse("axllent/mailpit"))
+            .withExposedPorts(1025, 8025);
+
+    static {
+        MYSQL.start();
+        MAILPIT.start();
+    }
+
+
+    private SharedContainers() {
+    }
+
+}

backend/src/test/java/team/projectpulse/activity/ActivityIntegrationTest.java

@@ -1,26 +1,17 @@
 package team.projectpulse.activity;
 
 import tools.jackson.databind.json.JsonMapper;
-import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
-import org.testcontainers.containers.MySQLContainer;
-import org.testcontainers.junit.jupiter.Container;
-import org.testcontainers.junit.jupiter.Testcontainers;
-import org.testcontainers.utility.DockerImageName;
+import team.projectpulse.AbstractIntegrationTest;
 import team.projectpulse.system.StatusCode;
 import org.hamcrest.Matchers;
 import org.json.JSONObject;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
-import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
-import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
-import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
-import org.springframework.test.annotation.DirtiesContext;
-import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MvcResult;
 import org.springframework.test.web.servlet.ResultActions;
@@ -36,13 +27,8 @@
 import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 
-@SpringBootTest
-@Testcontainers
-@AutoConfigureMockMvc
 @DisplayName("Integration tests for Activity API endpoints")
-@Tag("integration")
-@ActiveProfiles(value = "dev")
-public class ActivityIntegrationTest {
+public class ActivityIntegrationTest extends AbstractIntegrationTest {
 
     @Autowired
     MockMvc mockMvc;
@@ -61,10 +47,6 @@ public class ActivityIntegrationTest {
     @Value("${api.endpoint.base-url}")
     String baseUrl;
 
-    @Container
-    @ServiceConnection
-    static MySQLContainer<?> mysql = new MySQLContainer<>(DockerImageName.parse("mysql:8.0"));
-
     @BeforeEach
     void setUp() throws Exception {
         ResultActions resultActions = this.mockMvc.perform(post(this.baseUrl + "/users/login").with(httpBasic("b.wei@abc.edu", "123456"))); // httpBasic() is from spring-security-test.
@@ -228,7 +210,6 @@ void testStudentJanaFindActivityById() throws Exception {
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
     void testStudentJohnAddActivity() throws Exception {
         // Given
         Map<String, Object> activityDto = new HashMap<>();
@@ -259,7 +240,6 @@ void testStudentJohnAddActivity() throws Exception {
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
     void testStudentJohnUpdatesOwnActivity() throws Exception {
         // Given
         Map<String, Object> activityDto = new HashMap<>();
@@ -310,7 +290,6 @@ void testStudentUpdatesAnotherStudentsActivity() throws Exception {
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
     void testStudentJohnDeletesOwnActivity() throws Exception {
         this.mockMvc.perform(delete(this.baseUrl + "/activities/1").accept(MediaType.APPLICATION_JSON).header(HttpHeaders.AUTHORIZATION, this.studentJohnToken))
                 .andExpect(jsonPath("$.flag").value(true))

backend/src/test/java/team/projectpulse/course/CourseIntegrationTest.java

@@ -1,34 +1,22 @@
 package team.projectpulse.course;
 
 import tools.jackson.databind.json.JsonMapper;
-import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
-import org.testcontainers.containers.MySQLContainer;
+import team.projectpulse.AbstractIntegrationTest;
 import team.projectpulse.system.StatusCode;
 import org.hamcrest.Matchers;
 import org.json.JSONObject;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
-import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
-import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
-import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
-import org.springframework.test.annotation.DirtiesContext;
-import org.springframework.test.context.ActiveProfiles;
-import org.springframework.test.context.DynamicPropertyRegistry;
-import org.springframework.test.context.DynamicPropertySource;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MvcResult;
 import org.springframework.test.web.servlet.ResultActions;
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
-import org.testcontainers.containers.GenericContainer;
-import org.testcontainers.junit.jupiter.Container;
-import org.testcontainers.junit.jupiter.Testcontainers;
-import org.testcontainers.utility.DockerImageName;
 
 import java.util.HashMap;
 import java.util.Map;
@@ -38,13 +26,8 @@
 import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 
-@SpringBootTest
-@Testcontainers
-@AutoConfigureMockMvc
 @DisplayName("Integration tests for Course API endpoints")
-@Tag("integration")
-@ActiveProfiles(value = "dev")
-class CourseIntegrationTest {
+class CourseIntegrationTest extends AbstractIntegrationTest {
 
     @Autowired
     MockMvc mockMvc;
@@ -61,21 +44,6 @@ class CourseIntegrationTest {
     @Value("${api.endpoint.base-url}")
     String baseUrl;
 
-    @Container
-    @ServiceConnection
-    static MySQLContainer<?> mysql = new MySQLContainer<>(DockerImageName.parse("mysql:8.0"));
-
-    @Container
-    static final GenericContainer<?> mailpit = new GenericContainer<>(DockerImageName.parse("axllent/mailpit"))
-            .withExposedPorts(1025, 8025);
-
-
-    @DynamicPropertySource
-    static void setMailpitProperties(DynamicPropertyRegistry registry) {
-        registry.add("spring.mail.host", mailpit::getHost);
-        registry.add("spring.mail.port", () -> mailpit.getMappedPort(1025));
-    }
-
     @BeforeEach
     void setUp() throws Exception {
         ResultActions resultActions = this.mockMvc.perform(post(this.baseUrl + "/users/login").with(httpBasic("b.wei@abc.edu", "123456"))); // httpBasic() is from spring-security-test.
@@ -185,7 +153,7 @@ void adminTimFindCourseById() throws Exception {
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
+
     void adminBingyangAddCourse() throws Exception {
         // Given
         Map<String, String> courseDto = new HashMap<>();
@@ -219,7 +187,7 @@ void instructorBillAddCourse() throws Exception {
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
+
     void adminBingyangUpdateCourse() throws Exception {
         // Given
         Map<String, String> courseDto = new HashMap<>();

backend/src/test/java/team/projectpulse/evaluation/EvaluationIntegrationTest.java

@@ -1,29 +1,20 @@
 package team.projectpulse.evaluation;
 
 import tools.jackson.databind.json.JsonMapper;
-import org.springframework.boot.testcontainers.service.connection.ServiceConnection;
 import org.springframework.test.context.bean.override.mockito.MockitoSpyBean;
-import org.testcontainers.containers.MySQLContainer;
-import org.testcontainers.junit.jupiter.Container;
-import org.testcontainers.junit.jupiter.Testcontainers;
-import org.testcontainers.utility.DockerImageName;
+import team.projectpulse.AbstractIntegrationTest;
 import team.projectpulse.evaluation.dto.PeerEvaluationDto;
 import team.projectpulse.evaluation.dto.RatingDto;
 import team.projectpulse.system.StatusCode;
 import org.hamcrest.Matchers;
 import org.json.JSONObject;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.DisplayName;
-import org.junit.jupiter.api.Tag;
 import org.junit.jupiter.api.Test;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
-import org.springframework.boot.webmvc.test.autoconfigure.AutoConfigureMockMvc;
-import org.springframework.boot.test.context.SpringBootTest;
 import org.springframework.http.HttpHeaders;
 import org.springframework.http.MediaType;
-import org.springframework.test.annotation.DirtiesContext;
-import org.springframework.test.context.ActiveProfiles;
 import org.springframework.test.web.servlet.MockMvc;
 import org.springframework.test.web.servlet.MvcResult;
 import org.springframework.test.web.servlet.ResultActions;
@@ -41,13 +32,8 @@
 import static org.springframework.test.web.servlet.result.MockMvcResultHandlers.print;
 import static org.springframework.test.web.servlet.result.MockMvcResultMatchers.jsonPath;
 
-@SpringBootTest
-@Testcontainers
-@AutoConfigureMockMvc
 @DisplayName("Integration tests for Evaluation API endpoints")
-@Tag("integration")
-@ActiveProfiles(value = "dev")
-public class EvaluationIntegrationTest {
+public class EvaluationIntegrationTest extends AbstractIntegrationTest {
 
     /**
      * @MockitoSpyBean creates a Mockito spy and registers it as the active Spring bean.
@@ -74,10 +60,6 @@ public class EvaluationIntegrationTest {
     @Value("${api.endpoint.base-url}")
     String baseUrl;
 
-    @Container
-    @ServiceConnection
-    static MySQLContainer<?> mysql = new MySQLContainer<>(DockerImageName.parse("mysql:8.0"));
-
 
     @BeforeEach
     void setUp() throws Exception {
@@ -101,7 +83,7 @@ void setUp() throws Exception {
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
+
     void testStudentJohnAddEvaluation() throws Exception {
         List<RatingDto> ratingDtos = List.of(
                 new RatingDto(null, 1, 4.0),
@@ -265,7 +247,7 @@ void testEvaluatorJohnGetsEvaluationsByWrongEvaluatorIdAndWeek() throws Exceptio
     }
 
     @Test
-    @DirtiesContext(methodMode = DirtiesContext.MethodMode.AFTER_METHOD)
+
     void testEvaluatorJohnUpdatesOwnEvaluation() throws Exception {
         List<RatingDto> ratingDtos = List.of(
                 new RatingDto(1, 1, 4.0),