code: def test_single_timeseries_no_horizon_no_n(self):
      with pytest.raises(AttributeError):
          # even if the default axis is 0, but since it is a single timeseries, default axis is 1
          train_test_split(
              constant_timeseries(value=123, length=10),
              test_size=2,
              vertical_split_type=MODEL_AWARE,
          )
  
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 17 for calling the TestClassTrainTestSplit obj's underlying member method code with example usage: obj.test_single_timeseries_no_horizon_no_n() without return types