@Override
      public boolean shouldScheduleTask(TaskInfo taskInfo) {
        shouldScheduleTaskTriggered = true;
        lastShouldScheduleTaskResult = super.shouldScheduleTask(taskInfo);
        return lastShouldScheduleTaskResult;
      }
Note: this only works for testing the lack of invocations from the main thread.
llap-tez/src/test/org/apache/hadoop/hive/llap/tezplugins/TestLlapTaskSchedulerService.java