code: def test_multiplex_or_dunder():
      """Test that the MultiplexTransforemer magic "|" dunder works.
  
      A MultiplexTransformer can be created by using the "|" dunder method on either
      transformer or MultiplexTransformer objects. Here we test that it performs as
      expected on all the use cases, and raises the expected error in some others.
      """
      # test a simple | example with two transformers:
      multiplex_two_transformers = ExponentTransformer(
          2
      ) | ExponentTransformer(3)
      assert isinstance(
          multiplex_two_transformers, MultiplexTransformer
      )
      assert len(multiplex_two_transformers.transformers) == 2
      # now test that | also works on two MultiplexTransformers:
      multiplex_one = MultiplexTransformer(
          [
              ("exp_2", ExponentTransformer(2)),
              ("exp_3", ExponentTransformer(3)),
          ]
      )
      multiplex_two = MultiplexTransformer(
          [
              ("exp_4", ExponentTransformer(4)),
              ("exp_5", ExponentTransformer(5)),
          ]
      )
  
      multiplex_two_multiplex = multiplex_one | multiplex_two
      assert isinstance(multiplex_two_multiplex, MultiplexTransformer)
      assert len(multiplex_two_multiplex.transformers) == 4
      # last we will check 3 transformers with the same name - should check both that
      # MultiplexTransformer | transformer works, and that ensure_unique_names works
      multiplex_same_name_three_test = (
          ExponentTransformer(2)
          | ExponentTransformer(3)
          | ExponentTransformer(4)
      )
      assert isinstance(
          multiplex_same_name_three_test, MultiplexTransformer
      )
      assert len(multiplex_same_name_three_test._transformers) == 3
      transformer_param_names = (
          multiplex_same_name_three_test._get_estimator_names(
              multiplex_same_name_three_test._transformers
          )
      )
      assert len(set(transformer_param_names)) == 3
  
      # test we get a ValueError if we try to | with anything else:
      with pytest.raises(TypeError):
          multiplex_one | "this shouldn't work"
  
file_path: sktime/sktime/transformations/tests/test_multiplexer.py
imports: import numpy
  import pytest
  from numpy.testing import assert_array_equal
  from sklearn.base import clone
  from sktime.datasets import load_shampoo_sales
  from sktime.forecasting.compose import TransformedTargetForecaster
  from sktime.forecasting.model_evaluation import evaluate
  from sktime.forecasting.model_selection import ForecastingGridSearchCV
  from sktime.forecasting.naive import NaiveForecaster
  from sktime.split import ExpandingWindowSplitter
  from sktime.transformations.compose import MultiplexTransformer
  from sktime.transformations.series.exponent import ExponentTransformer
  from sktime.utils.validation.forecasting import check_scoring
label_desc: Use image node_id 4 for calling a global function with example usage: test_multiplex_or_dunder() without return types