test(gax): use FakeApiClock in DirectRetryingExecutorTest to avoid Thread.sleep (#14705)

Use FakeApiClock and RecordingScheduler in ScheduledRetryingExecutorTest
so non-concurrent retry tests execute deterministically without
sleeping. Isolate asynchronous polling and cancellation tests to use
per-iteration local ScheduledExecutorService instances and NanoClock.
Make RecordingScheduler stubbings lenient to avoid
UnnecessaryStubbingException when recorded metrics are not queried.

Fixes
[#13535](#14625)

Author: lqiu96

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/retrying/AbstractRetryingExecutorTest.java

@@ -45,6 +45,7 @@
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.verifyNoMoreInteractions;
 
+import com.google.api.core.ApiClock;
 import com.google.api.core.ApiFuture;
 import com.google.api.core.NanoClock;
 import com.google.api.gax.retrying.FailingCallable.CustomException;
@@ -102,6 +103,10 @@ protected abstract RetryingExecutorWithContext<String> getExecutor(
   protected abstract RetryAlgorithm<String> getAlgorithm(
       RetrySettings retrySettings, int apocalypseCountDown, RuntimeException apocalypseException);
 
+  protected ApiClock getClock() {
+    return NanoClock.getDefaultClock();
+  }
+
   protected <T> void busyWaitForInitialResult(RetryingFuture<T> future, java.time.Duration timeout)
       throws TimeoutException {
     Stopwatch watch = Stopwatch.createStarted();
@@ -356,7 +361,7 @@ void testPollExceptionByPollAlgorithm(boolean withCustomRetrySettings) throws Ex
                 useContextRetrySettings
                     ? withCustomRetrySettings ? FAILING_RETRY_SETTINGS : FAST_RETRY_SETTINGS
                     : retrySettings,
-                NanoClock.getDefaultClock()));
+                getClock()));
 
     RetryingExecutorWithContext<String> executor = getExecutor(retryAlgorithm);
     FailingCallable callable = new FailingCallable(6, "request", "FAILURE", tracer);

sdk-platform-java/gax-java/gax/src/test/java/com/google/api/gax/retrying/DirectRetryingExecutorTest.java

@@ -29,20 +29,41 @@
  */
 package com.google.api.gax.retrying;
 
-import com.google.api.core.CurrentMillisClock;
+import com.google.api.core.ApiClock;
+import com.google.api.gax.core.FakeApiClock;
+import java.time.Duration;
 
 class DirectRetryingExecutorTest extends AbstractRetryingExecutorTest {
 
+  // ExponentialRetryAlgorithm and ExponentialPollAlgorithm only compute relative elapsed time
+  // deltas against firstAttemptStartTimeNanos (clock.nanoTime() - firstAttemptStartTimeNanos)
+  // and never treat 0L as a special sentinel value.
+  private final FakeApiClock clock = new FakeApiClock(0L);
+
+  @Override
+  protected ApiClock getClock() {
+    return clock;
+  }
+
   @Override
   protected RetryingExecutorWithContext<String> getExecutor(RetryAlgorithm<String> retryAlgorithm) {
-    return new DirectRetryingExecutor<>(retryAlgorithm);
+    return new DirectRetryingExecutor<String>(retryAlgorithm) {
+      // Advance the fake clock instead of sleeping the current thread so that retry delays
+      // are simulated deterministically without wall-clock pauses on slow CI VMs.
+      @Override
+      protected void sleep(Duration delay) {
+        if (!delay.isZero() && !delay.isNegative()) {
+          clock.incrementNanoTime(delay.toNanos());
+        }
+      }
+    };
   }
 
   @Override
   protected RetryAlgorithm<String> getAlgorithm(
       RetrySettings retrySettings, int apocalypseCountDown, RuntimeException apocalypseException) {
     return new RetryAlgorithm<>(
         new TestResultRetryAlgorithm<String>(apocalypseCountDown, apocalypseException),
-        new ExponentialRetryAlgorithm(retrySettings, CurrentMillisClock.getDefaultClock()));
+        new ExponentialRetryAlgorithm(retrySettings, clock));
   }
 }