Development: Reduce flakiness of server tests

src/test/java/de/tum/cit/aet/artemis/communication/notification/PushNotificationResourceTest.java

@@ -8,7 +8,6 @@
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
-import org.junit.jupiter.api.TestInstance;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.http.HttpStatus;
 import org.springframework.security.test.context.support.WithMockUser;
@@ -24,7 +23,6 @@
 import de.tum.cit.aet.artemis.core.user.util.UserUtilService;
 import de.tum.cit.aet.artemis.shared.base.AbstractSpringIntegrationIndependentTest;
 
-@TestInstance(TestInstance.Lifecycle.PER_CLASS)
 class PushNotificationResourceTest extends AbstractSpringIntegrationIndependentTest {
 
     @Autowired

src/test/java/de/tum/cit/aet/artemis/programming/icl/LocalVCLocalCIIntegrationTest.java

@@ -34,9 +34,12 @@
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInstance;
+import org.junit.jupiter.api.parallel.Execution;
+import org.junit.jupiter.api.parallel.ExecutionMode;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.beans.factory.annotation.Qualifier;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.http.HttpStatus;
 import org.springframework.security.test.context.support.WithMockUser;
@@ -68,7 +71,18 @@
  * This class contains integration tests for the base repositories (template, solution, tests) and the different types of assignment repositories (student assignment, teaching
  * assistant assignment, instructor assignment).
  */
+
+// TestInstance.Lifecycle.PER_CLASS allows all test methods in this class to share the same instance of the test class.
+// This reduces the overhead of repeatedly creating and tearing down a new Spring application context for each test method.
+// This is especially useful when the test setup is expensive or when we want to share resources, such as database connections or mock objects, across multiple tests.
+// In this case, we want to share the same GitService and UsernamePasswordCredentialsProvider.
 @TestInstance(TestInstance.Lifecycle.PER_CLASS)
+
+// ExecutionMode.SAME_THREAD ensures that all tests within this class are executed sequentially in the same thread, rather than in parallel or in a different thread.
+// This is important in the context of LocalCI because it avoids potential race conditions or inconsistencies that could arise if multiple test methods are executed
+// concurrently. For example, it prevents overloading the LocalCI's result processing system with too many build job results at the same time, which could lead to flaky tests
+// or timeouts. By keeping everything in the same thread, we maintain more predictable and stable test behavior, while not increasing the test execution time significantly.
+@Execution(ExecutionMode.SAME_THREAD)
 class LocalVCLocalCIIntegrationTest extends AbstractLocalCILocalVCIntegrationTest {
 
     private static final Logger log = LoggerFactory.getLogger(LocalVCLocalCIIntegrationTest.class);
@@ -86,6 +100,7 @@ class LocalVCLocalCIIntegrationTest extends AbstractLocalCILocalVCIntegrationTes
     private SharedQueueProcessingService sharedQueueProcessingService;
 
     @Autowired
+    @Qualifier("hazelcastInstance")
     private HazelcastInstance hazelcastInstance;
 
     @Value("${artemis.user-management.internal-admin.username}")

src/test/java/de/tum/cit/aet/artemis/programming/icl/ProgrammingExerciseLocalVCLocalCIIntegrationTest.java

@@ -24,6 +24,8 @@
 import org.junit.jupiter.api.Nested;
 import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.TestInstance;
+import org.junit.jupiter.api.parallel.Execution;
+import org.junit.jupiter.api.parallel.ExecutionMode;
 import org.springframework.beans.factory.annotation.Autowired;
 import org.springframework.beans.factory.annotation.Value;
 import org.springframework.http.HttpStatus;
@@ -48,7 +50,17 @@
 import de.tum.cit.aet.artemis.programming.util.ProgrammingExerciseUtilService;
 import de.tum.cit.aet.artemis.shared.base.AbstractSpringIntegrationLocalCILocalVCTest;
 
+// TestInstance.Lifecycle.PER_CLASS allows all test methods in this class to share the same instance of the test class.
+// This reduces the overhead of repeatedly creating and tearing down a new Spring application context for each test method.
+// This is especially useful when the test setup is expensive or when we want to share resources, such as database connections or mock objects, across multiple tests.
+// In this case, we want to share the same GitService and UsernamePasswordCredentialsProvider.
 @TestInstance(TestInstance.Lifecycle.PER_CLASS)
+
+// ExecutionMode.SAME_THREAD ensures that all tests within this class are executed sequentially in the same thread, rather than in parallel or in a different thread.
+// This is important in the context of LocalCI because it avoids potential race conditions or inconsistencies that could arise if multiple test methods are executed
+// concurrently. For example, it prevents overloading the LocalCI's result processing system with too many build job results at the same time, which could lead to flaky tests
+// or timeouts. By keeping everything in the same thread, we maintain more predictable and stable test behavior, while not increasing the test execution time significantly.
+@Execution(ExecutionMode.SAME_THREAD)
 class ProgrammingExerciseLocalVCLocalCIIntegrationTest extends AbstractSpringIntegrationLocalCILocalVCTest {
 
     private static final String TEST_PREFIX = "progexlocalvclocalci";