code: def test_horiz_split_overindexing_train_set(self):
      train_set, test_set = train_test_split(
          make_dataset(8, 10), lazy=True
      )
      with pytest.raises(IndexError) as err:
          train_set[6]
      assert (
          str(err.value)
          == "Exceeded the size of the training sequence."
      )
  
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 8 for calling the TestClassTrainTestSplit obj's underlying member method code with example usage: obj.test_horiz_split_overindexing_train_set() without return types