Unit Testing @Scheduled and @Async Methods

Overview

This skill provides patterns for unit testing @Scheduled and @Async methods using JUnit 5. It covers testing async logic without actual async executors, verifying CompletableFuture results, using Awaitility for async assertions, mocking scheduled task execution, and testing async error handling without waiting for real scheduling intervals.

When to Use

Use this skill when:

• Testing @Scheduled method logic
• Testing @Async method behavior
• Verifying CompletableFuture results
• Testing async error handling
• Want fast tests without actual scheduling
• Testing background task logic in isolation

Instructions

1. Test async methods directly: Call @Async methods directly instead of relying on Spring’s async executor
2. Use CompletableFuture.get(): Wait for async operations to complete with explicit timeout
3. Mock async dependencies: Use @Mock for services that async methods depend on
4. Use Awaitility for assertions: Apply Awaitility.await() when testing actual async behavior
5. Test scheduled methods directly: Call @Scheduled methods directly instead of waiting for cron expressions
6. Verify mock interactions: Ensure dependencies were called correctly after async completion
7. Test exception handling: Verify exceptions in async methods propagate correctly
8. Set appropriate timeouts: Always use timeout with CompletableFuture.get() to avoid hanging tests

Examples

Setup: Async/Scheduled Testing

Maven

<dependency>
  <groupId>org.springframework.boot</groupId>
  <artifactId>spring-boot-starter</artifactId>
</dependency>
<dependency>
  <groupId>org.junit.jupiter</groupId>
  <artifactId>junit-jupiter</artifactId>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.awaitility</groupId>
  <artifactId>awaitility</artifactId>
  <scope>test</scope>
</dependency>
<dependency>
  <groupId>org.assertj</groupId>
  <artifactId>assertj-core</artifactId>
  <scope>test</scope>
</dependency>

Gradle

dependencies {
  implementation("org.springframework.boot:spring-boot-starter")
  testImplementation("org.junit.jupiter:junit-jupiter")
  testImplementation("org.awaitility:awaitility")
  testImplementation("org.assertj:assertj-core")
}

Testing @Async Methods

Basic Async Testing with CompletableFuture

// Service with async methods
@Service
public class EmailService {

  @Async
  public CompletableFuture<Boolean> sendEmailAsync(String to, String subject) {
    return CompletableFuture.supplyAsync(() -> {
      // Simulate email sending
      System.out.println("Sending email to " + to);
      return true;
    });
  }

  @Async
  public void notifyUser(String userId) {
    System.out.println("Notifying user: " + userId);
  }
}

// Unit test
import java.util.concurrent.CompletableFuture;
import static org.assertj.core.api.Assertions.*;

class EmailServiceAsyncTest {

  @Test
  void shouldReturnCompletedFutureWhenSendingEmail() throws Exception {
    EmailService service = new EmailService();

    CompletableFuture<Boolean> result = service.sendEmailAsync("test@example.com", "Hello");

    Boolean success = result.get(); // Wait for completion
    assertThat(success).isTrue();
  }

  @Test
  void shouldCompleteWithinTimeout() {
    EmailService service = new EmailService();

    CompletableFuture<Boolean> result = service.sendEmailAsync("test@example.com", "Hello");

    assertThat(result)
      .isCompletedWithValue(true);
  }
}

Testing Async with Mocked Dependencies

Async Service with Dependencies

@Service
public class UserNotificationService {

  private final EmailService emailService;
  private final SmsService smsService;

  public UserNotificationService(EmailService emailService, SmsService smsService) {
    this.emailService = emailService;
    this.smsService = smsService;
  }

  @Async
  public CompletableFuture<String> notifyUserAsync(String userId) {
    return CompletableFuture.supplyAsync(() -> {
      emailService.send(userId);
      smsService.send(userId);
      return "Notification sent";
    });
  }
}

// Unit test
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
class UserNotificationServiceAsyncTest {

  @Mock
  private EmailService emailService;

  @Mock
  private SmsService smsService;

  @InjectMocks
  private UserNotificationService notificationService;

  @Test
  void shouldNotifyUserAsynchronously() throws Exception {
    CompletableFuture<String> result = notificationService.notifyUserAsync("user123");

    String message = result.get();
    assertThat(message).isEqualTo("Notification sent");

    verify(emailService).send("user123");
    verify(smsService).send("user123");
  }

  @Test
  void shouldHandleAsyncExceptionGracefully() {
    doThrow(new RuntimeException("Email service failed"))
      .when(emailService).send(any());

    CompletableFuture<String> result = notificationService.notifyUserAsync("user123");

    assertThatThrownBy(result::get)
      .isInstanceOf(ExecutionException.class)
      .hasCauseInstanceOf(RuntimeException.class);
  }
}

Testing @Scheduled Methods

Mock Task Execution

// Scheduled task
@Component
public class DataRefreshTask {

  private final DataRepository dataRepository;

  public DataRefreshTask(DataRepository dataRepository) {
    this.dataRepository = dataRepository;
  }

  @Scheduled(fixedDelay = 60000)
  public void refreshCache() {
    List<Data> data = dataRepository.findAll();
    // Update cache
  }

  @Scheduled(cron = "0 0 * * * *") // Every hour
  public void cleanupOldData() {
    dataRepository.deleteOldData(LocalDateTime.now().minusDays(30));
  }
}

// Unit test - test logic without actual scheduling
import org.junit.jupiter.api.extension.ExtendWith;
import org.mockito.InjectMocks;
import org.mockito.Mock;
import org.mockito.junit.jupiter.MockitoExtension;

@ExtendWith(MockitoExtension.class)
class DataRefreshTaskTest {

  @Mock
  private DataRepository dataRepository;

  @InjectMocks
  private DataRefreshTask dataRefreshTask;

  @Test
  void shouldRefreshCacheFromRepository() {
    List<Data> expectedData = List.of(new Data(1L, "item1"));
    when(dataRepository.findAll()).thenReturn(expectedData);

    dataRefreshTask.refreshCache(); // Call method directly

    verify(dataRepository).findAll();
  }

  @Test
  void shouldCleanupOldData() {
    LocalDateTime cutoffDate = LocalDateTime.now().minusDays(30);

    dataRefreshTask.cleanupOldData();

    verify(dataRepository).deleteOldData(any(LocalDateTime.class));
  }
}

Testing Async with Awaility

Wait for Async Completion

import org.awaitility.Awaitility;
import java.util.concurrent.atomic.AtomicInteger;

@Service
public class BackgroundWorker {

  private final AtomicInteger processedCount = new AtomicInteger(0);

  @Async
  public void processItems(List<String> items) {
    items.forEach(item -> {
      // Process item
      processedCount.incrementAndGet();
    });
  }

  public int getProcessedCount() {
    return processedCount.get();
  }
}

class AwaitilityAsyncTest {

  @Test
  void shouldProcessAllItemsAsynchronously() {
    BackgroundWorker worker = new BackgroundWorker();
    List<String> items = List.of("item1", "item2", "item3");

    worker.processItems(items);

    // Wait for async operation to complete (up to 5 seconds)
    Awaitility.await()
      .atMost(Duration.ofSeconds(5))
      .pollInterval(Duration.ofMillis(100))
      .untilAsserted(() -> {
        assertThat(worker.getProcessedCount()).isEqualTo(3);
      });
  }

  @Test
  void shouldTimeoutWhenProcessingTakesTooLong() {
    BackgroundWorker worker = new BackgroundWorker();
    List<String> items = List.of("item1", "item2", "item3");

    worker.processItems(items);

    assertThatThrownBy(() -> 
      Awaitility.await()
        .atMost(Duration.ofMillis(100))
        .until(() -> worker.getProcessedCount() == 10)
    ).isInstanceOf(ConditionTimeoutException.class);
  }
}

Testing Async Error Handling

Handle Exceptions in Async Methods

@Service
public class DataProcessingService {

  @Async
  public CompletableFuture<Boolean> processDataAsync(String data) {
    return CompletableFuture.supplyAsync(() -> {
      if (data == null || data.isEmpty()) {
        throw new IllegalArgumentException("Data cannot be empty");
      }
      // Process data
      return true;
    });
  }

  @Async
  public CompletableFuture<String> safeFetchData(String id) {
    return CompletableFuture.supplyAsync(() -> {
      try {
        return fetchData(id);
      } catch (Exception e) {
        return "Error: " + e.getMessage();
      }
    });
  }
}

class AsyncErrorHandlingTest {

  @Test
  void shouldPropagateExceptionFromAsyncMethod() {
    DataProcessingService service = new DataProcessingService();

    CompletableFuture<Boolean> result = service.processDataAsync(null);

    assertThatThrownBy(result::get)
      .isInstanceOf(ExecutionException.class)
      .hasCauseInstanceOf(IllegalArgumentException.class)
      .hasMessageContaining("Data cannot be empty");
  }

  @Test
  void shouldHandleExceptionGracefullyWithFallback() throws Exception {
    DataProcessingService service = new DataProcessingService();

    CompletableFuture<String> result = service.safeFetchData("invalid");

    String message = result.get();
    assertThat(message).startsWith("Error:");
  }
}

Testing Scheduled Task Timing

Test Schedule Configuration

@Component
public class HealthCheckTask {

  private final HealthCheckService healthCheckService;
  private int executionCount = 0;

  public HealthCheckTask(HealthCheckService healthCheckService) {
    this.healthCheckService = healthCheckService;
  }

  @Scheduled(fixedRate = 5000) // Every 5 seconds
  public void checkHealth() {
    executionCount++;
    healthCheckService.check();
  }

  public int getExecutionCount() {
    return executionCount;
  }
}

class ScheduledTaskTimingTest {

  @Test
  void shouldExecuteTaskMultipleTimes() {
    HealthCheckService mockService = mock(HealthCheckService.class);
    HealthCheckTask task = new HealthCheckTask(mockService);

    // Execute manually multiple times
    task.checkHealth();
    task.checkHealth();
    task.checkHealth();

    assertThat(task.getExecutionCount()).isEqualTo(3);
    verify(mockService, times(3)).check();
  }
}

Best Practices

• Test async method logic directly without Spring async executor
• Use CompletableFuture.get() to wait for results in tests
• Mock dependencies that async methods use
• Test error paths for async operations
• Use Awaitility when testing actual async behavior is needed
• Mock scheduled tasks by calling methods directly in tests
• Verify task execution count for testing scheduling logic

Common Pitfalls

• Testing with actual @Async executor (use direct method calls instead)
• Not waiting for CompletableFuture completion in tests
• Forgetting to test exception handling in async methods
• Not mocking dependencies that async methods call
• Trying to test actual scheduling timing (test logic instead)

Constraints and Warnings

• @Async requires proxy: Spring’s @Async works via proxies; direct method calls bypass async behavior
• ThreadPoolTaskScheduler: Scheduled tasks use a thread pool; order of execution is not guaranteed
• CompletableFuture chaining: Chain operations carefully; exceptions in intermediate stages can be lost
• Awaitility timeout: Set reasonable timeouts; infinite waits can hang test suites
• Scheduled task timing: Don’t test actual cron/fixedRate timing; test the method logic directly
• Thread safety: Async code must be thread-safe; verify behavior under concurrent access
• @Async on same class: Calling @Async method from another method in same class won’t be async

Troubleshooting

CompletableFuture hangs in test: Ensure methods complete or set timeout with .get(timeout, unit).

Async method not executing: Call method directly instead of relying on @Async in tests.

Awaitility timeout: Increase timeout duration or reduce polling interval.

References

• Spring @Async Documentation
• Spring @Scheduled Documentation
• Awaitility Testing Library
• CompletableFuture API