@Test(expected = ExecutorManagerException.class)
public void testEnqueueDuplicateExecution() throws IOException,
    ExecutorManagerException {

  final Pair<ExecutionReference, ExecutableFlow> pair1 =
      createExecutablePair("exec1", 1);
  final QueuedExecutions queue = new QueuedExecutions(5);
  queue.enqueue(pair1.getSecond(), pair1.getFirst());
  queue.enqueue(pair1.getSecond(), pair1.getFirst());
}