code: def test_round_robin_batch_sampler(self):
      # no iter_to_set_epoch
      round_robin_iterator = RoundRobinBatchSampler().batchify(
          self.iter_dict
      )
      expected_items = ["1", "a", "2", "b", "3", "c", "4"]
      self._check_iterator(round_robin_iterator, expected_items)
  
      # iter_to_set_epoch = "A"
      round_robin_iterator = RoundRobinBatchSampler(
          iter_to_set_epoch="A"
      ).batchify(self.iter_dict)
      expected_items = [
          "1",
          "a",
          "2",
          "b",
          "3",
          "c",
          "4",
          "a",
          "5",
          "b",
      ]
      self._check_iterator(round_robin_iterator, expected_items)
  
file_path: pytext/pytext/data/test/batch_sampler_test.py
imports: import unittest
  from pytext.data import AlternatingRandomizedBatchSampler, EvalBatchSampler, RandomizedBatchSampler, RoundRobinBatchSampler
label_desc: Use image node_id 2 for calling the BatchSamplerTest obj's underlying member method code with example usage: obj.test_round_robin_batch_sampler() without return types