code: def test_horiz_split_last_index_train_set(self):
      train_set, test_set = train_test_split(
          make_dataset(8, 10), lazy=True
      )
      # no IndexError is thrown
      train_set[5]
  
imports: import pytest
  from darts.utils.model_selection import MODEL_AWARE, SIMPLE, train_test_split
  from darts.utils.timeseries_generation import constant_timeseries
label_desc: Use image node_id 9 for calling the TestClassTrainTestSplit obj's underlying member method code with example usage: obj.test_horiz_split_last_index_train_set() without return types