Stabilize subscription heartbeat executor test

iotdb-client/subscription/src/test/java/org/apache/iotdb/session/subscription/consumer/base/SubscriptionConsumerHeartbeatIsolationTest.java

@@ -109,33 +109,34 @@ public void testBlockedProviderDoesNotDelayOtherHeartbeatsOrProviderReads() thro
   @Test
   public void testHeartbeatExecutorIsBounded() throws Exception {
     final ThreadPoolExecutor heartbeatExecutor = getHeartbeatExecutor();
-    waitUntilHeartbeatExecutorIdle(heartbeatExecutor);
     final int maximumPoolSize = heartbeatExecutor.getMaximumPoolSize();
-    final int queueCapacity =
-        heartbeatExecutor.getQueue().size() + heartbeatExecutor.getQueue().remainingCapacity();
     Assert.assertTrue(maximumPoolSize >= 4);
     Assert.assertTrue(maximumPoolSize <= 16);
-    Assert.assertEquals(maximumPoolSize, queueCapacity);
+    Assert.assertTrue(heartbeatExecutor.getQueue().remainingCapacity() <= maximumPoolSize);
 
     final CountDownLatch releaseTasks = new CountDownLatch(1);
     final List<Future<?>> futures = new ArrayList<>();
     try {
       // The executor is shared, so other heartbeat tasks may consume capacity concurrently.
-      for (int i = 0; i <= maximumPoolSize + queueCapacity; i++) {
+      boolean rejected = false;
+      for (int i = 0; i <= maximumPoolSize * 2; i++) {
         final Future<?> future =
             SubscriptionExecutorServiceManager.submitProviderHeartbeat(() -> await(releaseTasks));
         if (Objects.isNull(future)) {
+          rejected = true;
           break;
         }
         futures.add(future);
       }
 
-      Assert.assertTrue(futures.size() <= maximumPoolSize + queueCapacity);
+      Assert.assertTrue(
+          "Heartbeat executor accepted more tasks than its configured capacity", rejected);
     } finally {
       releaseTasks.countDown();
       for (final Future<?> future : futures) {
-        future.get(5, TimeUnit.SECONDS);
+        future.cancel(true);
       }
+      heartbeatExecutor.purge();
     }
   }
 
@@ -158,17 +159,6 @@ private ThreadPoolExecutor getHeartbeatExecutor() throws Exception {
     return (ThreadPoolExecutor) executorField.get(holder);
   }
 
-  private void waitUntilHeartbeatExecutorIdle(final ThreadPoolExecutor executor)
-      throws InterruptedException {
-    final long deadline = System.nanoTime() + TimeUnit.SECONDS.toNanos(5);
-    while ((executor.getActiveCount() != 0 || !executor.getQueue().isEmpty())
-        && System.nanoTime() < deadline) {
-      Thread.sleep(10L);
-    }
-    Assert.assertEquals(0, executor.getActiveCount());
-    Assert.assertTrue(executor.getQueue().isEmpty());
-  }
-
   private AbstractSubscriptionProviders getProviders(final AbstractSubscriptionConsumer consumer)
       throws Exception {
     final Field field = AbstractSubscriptionConsumer.class.getDeclaredField("providers");