unit-test-scheduled-async

# 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 reach...