text: import pandas as pd
  import pytest
  
  from ballet.encoder import make_robust_encoder
  from ballet.eng import IdentityTransformer
  from ballet.util.testing import assert_series_equal
  
  with_encoder = pytest.mark.parametrize(
      'encoder',
      [
          None,
          lambda x: x,
          IdentityTransformer(),
          [None],
          [None, None],
      ]
  )
  
  
  @with_encoder
  def test_encoder_pipeline(encoder):
      encoder_pipeline = make_robust_encoder(encoder)
      y_df = pd.util.testing.makeFloatSeries()
      encoder_pipeline.fit(y_df)
      y = encoder_pipeline.transform(y_df)
      assert_series_equal(y, y_df)
  