code: def test_negative_test_start_index(self):
      with pytest.raises(AttributeError) as err:
          train_set, test_set = train_test_split(
              make_dataset(1, 10),
              axis=1,
              input_size=2,
              horizon=9,
              test_size=1,
              vertical_split_type=MODEL_AWARE,
          )
      assert (
          str(err.value)
          == "Not enough data to create training and test sets"
      )
  
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 15 for calling the TestClassTrainTestSplit obj's underlying member method code with example usage: obj.test_negative_test_start_index() without return types