code: def test_round_robin(self):
      readers = {
          "a": PlainTextReader(),
          "b": PlainTextReader(),
          "c": PlainTextReader(),
      }
  
      reader = InterleavingDatasetReader(readers)
      data_dir = self.FIXTURES_ROOT / "data"
  
      file_path = {
          "a": data_dir / "babi.txt",
          "b": data_dir / "conll2003.txt",
          "c": data_dir / "conll2003.txt",
      }
  
      instances = list(reader.read(file_path))
      first_three_keys = {
          instance.fields["dataset"].metadata
          for instance in instances[:3]
      }
      assert first_three_keys == {"a", "b", "c"}
  
      next_three_keys = {
          instance.fields["dataset"].metadata
          for instance in instances[3:6]
      }
      assert next_three_keys == {"a", "b", "c"}
  
imports: from typing import Iterable
  import pytest
  from allennlp.common.testing import AllenNlpTestCase
  from allennlp.data.dataset_readers import DatasetReader, InterleavingDatasetReader
  from allennlp.data.data_loaders import MultiProcessDataLoader
  from allennlp.data.fields import TextField
  from allennlp.data.instance import Instance
  from allennlp.data.token_indexers import SingleIdTokenIndexer
  from allennlp.data.tokenizers import SpacyTokenizer
  from allennlp.data.vocabulary import Vocabulary
label_desc: Use image node_id 1 for calling the TestInterleavingDatasetReader obj's underlying member method code with example usage: obj.test_round_robin() without return types