@Test
  public void monitorHandlesDefunctThread() {
    threadsMonitoringImpl = new ThreadsMonitoringImpl(null, 100000, TIME_LIMIT_MILLIS);
    final long threadID = Long.MAX_VALUE;

    AbstractExecutor absExtgroup = new PooledExecutorGroup(threadID);
    absExtgroup.setStartTime(absExtgroup.getStartTime() - TIME_LIMIT_MILLIS - 1);

    threadsMonitoringImpl.getMonitorMap().put(threadID, absExtgroup);

    assertTrue(threadsMonitoringImpl.getThreadsMonitoringProcess().mapValidation());
  }
Tests that indeed thread is considered stuck when it should
geode-core/src/test/java/org/apache/geode/internal/monitoring/ThreadsMonitoringImplTest.java