unit-test-scheduled-async

name: unit-test-scheduled-async description: Provides patterns for unit testing Spring @Scheduled and @Async methods using JUnit 5, CompletableFuture, Awaitility, and Mockito. Covers mocking task execution and timing, verifying execution counts, testing cron expressions, validating retry behavior, and simulating thread pool behavior. Use when testing background tasks, cron jobs, periodic execution, scheduled tasks, or thread pool behavior. allowed-tools: Read, Write, Bash, Glob, Grep

Unit Testing @Scheduled and @Async Methods

Overview

Patterns for unit testing Spring @Scheduled and @Async methods with JUnit 5. Test CompletableFuture results, use Awaitility for race conditions, mock scheduled task execution, and validate error handling — without waiting for real scheduling intervals.

When to Use

• Testing @Scheduled method logic
• Testing @Async method behavior
• Verifying CompletableFuture results
• Testing async error handling
• Testing cron expression logic without waiting for actual scheduling
• Validating thread pool behavior and execution counts
• Testing background task logic in isolation

Instructions

1. Call @Async methods directly — bypass Spring's async proxy; the annotation is irrelevant in unit tests
2. Mock dependencies with @Mock and @InjectMocks (Mockito)
3. Wait for completion — use CompletableFuture.get(timeout, unit) or await().atMost(...).untilAsserted(...)
4. Call @Scheduled methods directly — do not wait for cron/fixedRate; the annotation is ignored in unit tests
5. Test exception paths — verify ExecutionException wrapping on CompletableFuture.get()

Validation checkpoints:

• After CompletableFuture.get(), assert the returned value before verifying mock interactions
• If ExecutionException is thrown, check .getCause() to identify the root exception
• If Awaitility times out, increase atMost() duration or reduce pollInterval() until the condition is reachable
• After multiple task invocations, assert execution counts before verify() calls

Examples

Key patterns — complete examples in references/examples.md:

// @Async: call directly, wait with CompletableFuture.get(timeout, unit)
@Service
class EmailService {
  @Async
  public CompletableFuture<Boolean> sendEmailAsync(String to) {
    return CompletableFuture.supplyAsync(() -> true);
  }
}
@Test
void shouldReturnCompletedFuture() throws Exception {
  EmailService service = new EmailService();
  Boolean result = service.sendEmailAsync("test@example.com").get(5, TimeUnit.SECONDS);
  assertThat(result).isTrue();
}

// @Scheduled: call directly, mock the repository
@Component
class DataRefreshTask {
  @InjectMocks private DataRepository dataRepository;
  @Scheduled(fixedDelay = 60000) public void refreshCache() { /* ... */ }
}
@Test
void shouldRefreshCache() {
  when(dataRepository.findAll()).thenReturn(List.of(new Data(1L, "item1")));
  dataRefreshTask.refreshCache();
  verify(dataRepository).findAll();
}

// Awaitility: use for race conditions with shared mutable state
@Test
void shouldProcessAllItems() {
  BackgroundWorker worker = new BackgroundWorker();
  worker.processItems(List.of("item1", "item2", "item3"));
  Awaitility.await()
    .atMost(Duration.ofSeconds(5))
    .pollInterval(Duration.ofMillis(100))
    .untilAsserted(() -> assertThat(worker.getProcessedCount()).isEqualTo(3));
}

// Mocked dependencies with exception handling
@Test
void shouldHandleAsyncExceptionGracefully() {
  doThrow(new RuntimeException("Email failed")).when(emailService).send(any());
  CompletableFuture<String> result = service.notifyUserAsync("user123");
  assertThatThrownBy(result::get)
    .isInstanceOf(ExecutionException.class)
    .hasCauseInstanceOf(RuntimeException.class);
}

Full Maven/Gradle dependencies, additional test classes, and execution count patterns: see references/examples.md.

Best Practices

• Always set a timeout on CompletableFuture.get() to prevent hanging tests
• Mock all dependencies — never call real external services in unit tests
• Use Awaitility only for race conditions; prefer direct calls for simple async methods
• Test @Scheduled logic directly — the annotation is ignored in unit tests
• Assert values before verifying mock interactions; verify after async completion

Common Pitfalls

• Relying on Spring's async executor instead of calling methods directly
• Missing timeout on CompletableFuture.get()
• Forgetting to test exception propagation in async methods
• Not mocking dependencies that async methods invoke internally
• Waiting for actual cron/fixedRate timing instead of testing logic in isolation

Constraints and Warnings

• @Async self-invocation: calling @Async from another method in the same class executes synchronously — the Spring proxy is bypassed
• Thread pool ordering: ThreadPoolTaskScheduler does not guarantee execution order
• CompletableFuture chaining: exceptions in intermediate stages can be silently lost — test each stage
• Awaitility timeout: always set a reasonable atMost(); infinite waits hang the test suite
• No actual scheduling: @Scheduled is ignored in unit tests — call methods directly

References

• Spring @Async Documentation
• Spring @Scheduled Documentation
• Awaitility Testing Library
• CompletableFuture API
• Code examples: references/examples.md