code: def test_getitem(self):
      # given
  
      transformers = [
          self.PlusTenTransformer(name=f"+10 transformer{i}")
          for i in range(0, 10)
      ]
      p = Pipeline(transformers)
  
      # when & then
      # note : only compares string representations, since __getitem__() copies the transformers
      assert str(p[1]._transformers) == str([transformers[1]])
      assert str(p[4:8]._transformers) == str(transformers[4:8])
  
      with pytest.raises(ValueError):
          p["invalid attempt"]
  
imports: from typing import Any, Mapping
  import pytest
  from darts import TimeSeries
  from darts.dataprocessing import Pipeline
  from darts.dataprocessing.transformers import BaseDataTransformer, FittableDataTransformer, InvertibleDataTransformer, InvertibleMapper, Mapper
  from darts.utils.timeseries_generation import constant_timeseries
label_desc: Use image node_id 8 for calling the TestPipeline obj's underlying member method code with example usage: obj.test_getitem() without return types