code: def test_no_workers(self) -> None:
      datapipes = [
          _DummyDataReader(1000, str(idx)) for idx in range(10)
      ]
      with patch(
          "torchrec.datasets.utils.get_worker_info"
      ) as get_worker_info:
          get_worker_info.return_value = None
          dp = ParallelReadConcat(*datapipes)
          self.assertEqual(len(list(dp)), 10000)
  
imports: import random
  import unittest
  from typing import Any, Iterator, List, Tuple
  from unittest.mock import Mock, patch
  from torch.utils.data import IterDataPipe
  from torchrec.datasets.utils import idx_split_train_val, ParallelReadConcat, rand_split_train_val
label_desc: Use image node_id 2 for calling the TestParallelReadConcat obj's underlying member method code with example usage: obj.test_no_workers() without return types