fix(gax): use fake clock in ScheduledRetryingExecutorTest for robust and fast execution

[lqiu96]

Introduced FakeApiClock and RecordingScheduler to ScheduledRetryingExecutorTest to run most tests (including the flaky testSuccessWithFailuresGetAttempt) instantly without real-time delays.

Isolated tests that rely on asynchronous polling or cancellation to use local real executors and clocks, with increased timeout (10s) to avoid flakiness on slow VMs.

Made RecordingScheduler stubbings lenient to avoid UnnecessaryStubbingException in tests that do not query all recorded metrics.

Fixes: #13535

[gemini-code-assist]

Code Review

This pull request refactors the test suite in ScheduledRetryingExecutorTest to use a fake clock and introduces local scheduled executors for isolated test runs. It also applies Mockito.lenient() to mock configurations in RecordingScheduler to prevent strict stubbing errors. The review feedback suggests moving the creation and shutdown of the local executors inside the test loops for testSuccessWithFailuresPeekAttempt and testCancelOuterFutureAfterStart to ensure complete isolation between iterations and avoid potential test flakiness.

[gemini-code-assist]

Creating the localExecutor outside the loop means it is shared across all iterations of the test. If any tasks from a previous iteration are still executing or scheduled, they could interfere with subsequent iterations, leading to test flakiness or race conditions. Creating and shutting down the executor inside the loop ensures complete isolation between iterations.

    for (int executionsCount = 0; executionsCount < EXECUTIONS_COUNT; executionsCount++) {
      ScheduledExecutorService localExecutor = Executors.newSingleThreadScheduledExecutor();
      try {
        FailingCallable callable = new FailingCallable(15, "request", "SUCCESS", tracer);

        RetryingExecutorWithContext<String> executor =
            getRetryingExecutor(
                getAlgorithm(retrySettings, 0, null, NanoClock.getDefaultClock()), localExecutor);
        RetryingFuture<String> future =
            executor.createFuture(
                callable,
                FakeCallContext.createDefault().withTracer(tracer).withRetrySettings(retrySettings));
        callable.setExternalFuture(future);

        assertNull(future.peekAttemptResult());
        assertSame(future.peekAttemptResult(), future.peekAttemptResult());
        assertFalse(future.getAttemptResult().isDone());
        assertFalse(future.getAttemptResult().isCancelled());

        future.setAttemptFuture(executor.submit(future));

        final AtomicInteger failedAttempts = new AtomicInteger(0);
        final AtomicReference<ApiFuture<String>> lastSeenAttempt = new AtomicReference<>();
        await()
            .pollInterval(Duration.ofMillis(2))
            .atMost(Duration.ofSeconds(5))
            .until(
                () -> {
                  ApiFuture<String> attemptResult = future.peekAttemptResult();
                  if (attemptResult != null && attemptResult != lastSeenAttempt.get()) {
                    lastSeenAttempt.set(attemptResult);
                    assertTrue(attemptResult.isDone());
                    assertFalse(attemptResult.isCancelled());
                    try {
                      attemptResult.get();
                    } catch (ExecutionException e) {
                      if (e.getCause() instanceof CustomException) {
                        failedAttempts.incrementAndGet();
                      }
                    }
                  }
                  return future.isDone();
                });

        assertFutureSuccess(future);
        assertEquals(15, future.getAttemptSettings().getAttemptCount());
        assertTrue(failedAttempts.get() > 0);
      } finally {
        localExecutor.shutdownNow();
      }
    }

[gemini-code-assist]

Similar to the other test, creating the localExecutor outside the loop can lead to cross-iteration interference. Since this test verifies the number of cancellation attempts on the shared tracer, any delayed task from a previous iteration that runs late and invokes the tracer could cause the verification to fail. Creating and shutting down the executor inside the loop ensures complete isolation.

    for (int executionsCount = 0; executionsCount < EXECUTIONS_COUNT; executionsCount++) {
      ScheduledExecutorService localExecutor = Executors.newSingleThreadScheduledExecutor();
      try {
        FailingCallable callable = new FailingCallable(4, "request", "SUCCESS", tracer);
        RetryingExecutorWithContext<String> executor =
            getRetryingExecutor(
                getAlgorithm(retrySettings, 0, null, NanoClock.getDefaultClock()), localExecutor);
        RetryingFuture<String> future =
            executor.createFuture(
                callable,
                FakeCallContext.createDefault().withTracer(tracer).withRetrySettings(retrySettings));
        callable.setExternalFuture(future);
        future.setAttemptFuture(executor.submit(future));

        await()
            .atMost(Duration.ofSeconds(5))
            .until(
                () ->
                    future.getAttemptSettings() != null
                        && future.getAttemptSettings().getAttemptCount() > 0);

        boolean res = future.cancel(false);
        assertTrue(res);
        assertFutureCancel(future);

        // Verify that the cancelled future is traced. Every attempt increases the number
        // of cancellation attempts from the tracer.
        Mockito.verify(tracer, Mockito.times(executionsCount + 1)).attemptCancelled();

        // Assert that future has at least been attempted once
        // i.e. The future from executor.submit() has been run by the ScheduledExecutor
        assertTrue(future.getAttemptSettings().getAttemptCount() > 0);
        assertTrue(future.getAttemptSettings().getAttemptCount() < 4);
      } finally {
        localExecutor.shutdownNow();
      }
    }

[sonarqubecloud]

Quality Gate passed for 'gapic-generator-java-root'

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[sonarqubecloud]

Quality Gate passed for 'gapic-generator-java-root'

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud