@Override
    public List<Task<?>> getDependentTasks() {
      count++;
      System.err.println("YAH:getDepTasks got called!");
      (new Exception()).printStackTrace(System.err);
      LOG.info("YAH!getDepTasks", new Exception());
      return super.getDependentTasks();
    }
DependencyCollectionTask that counts how often getDependentTasks on it
(and thus, on its descendants) is called counted via Task.getDependentTasks.
It is used to wrap another task to intercept calls on it.
ql/src/test/org/apache/hadoop/hive/ql/exec/TestUtilities.java