code: def test_transform_fit(self):
      # given
      data = constant_timeseries(value=0, length=3)
      transformers = [
          self.DataTransformerMock1() for _ in range(10)
      ] + [self.DataTransformerMock2() for _ in range(10)]
      p = Pipeline(transformers)
  
      # when
      _ = p.fit_transform(data)
  
      # then
      for t in transformers:
          assert t.transform_called
      for i in range(10):
          assert not transformers[i].fit_called
      for i in range(10, 20):
          assert transformers[i].fit_called
  
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 6 for calling the TestPipeline obj's underlying member method code with example usage: obj.test_transform_fit() without return types