code: def test_SetSingleBatch(self) -> None:
      data = Data(df=self.df)
      merged_data = set_single_trial(data)
      self.assertTrue((merged_data.df["trial_index"] == 0).all())
  
      data = Data(
          df=pd.DataFrame(
              [
                  {
                      "arm_name": "0_1",
                      "mean": 3.7,
                      "sem": 0.5,
                      "metric_name": "b",
                  }
              ]
          )
      )
      merged_data = set_single_trial(data)
      self.assertTrue("trial_index" not in merged_data.df)
  
imports: import random
  import pandas
  from ax.core.data import clone_without_metrics, custom_data_class, Data, set_single_trial
  from ax.utils.common.testutils import TestCase
  from ax.utils.common.timeutils import current_timestamp_in_millis
label_desc: Use image node_id 5 for calling the DataTest obj's underlying member method code with example usage: obj.test_SetSingleBatch() without return types