code: def test_return_on_first_completed(self):
      def waiter():
          self.assertTrue(self._manager.wait_for_stop())
  
      def worker():
          pass
  
      self._manager.thread_worker("waiter", waiter)
      self._manager.thread_worker("worker", worker)
      self._manager.wait(return_on_first_completed=True)
  
imports: import os
  import signal
  import threading
  import time
  from absl.testing import absltest
  from launchpad.launch import worker_manager
  import mock
label_desc: Use image node_id 10 for calling the WorkerManagerTest obj's underlying member method code with example usage: obj.test_return_on_first_completed() without return types