message: Use coordinator.join instead of joining threads to make sure thread exceptions are reliably thrown.
diff: @@ -530,8 +530,7 @@ class DynamicClusterTest(test.TestCase, parameterized.TestCase):
  threads.append(threading.Thread(target=update_server_def_fn))
  for t in threads:
  t.start()
  - for t in threads:
  - t.join()
  + self._coord.join(threads)
  for result in results:
  np.testing.assert_array_equal([[2, 2], [2, 2]], result)
  