code: def test_power_transformer():
      """Tests basic PowerTransformer functionality."""
  
      # yeo-johnson
      col_a = [-1, 0]
      col_b = [0, 1]
      in_df = pd.DataFrame.from_dict({"A": col_a, "B": col_b})
      ds = ray.data.from_pandas(in_df)
  
      # yeo-johnson power=0
      transformer = PowerTransformer(["A", "B"], power=0)
      transformed = transformer.transform(ds)
      out_df = transformed.to_pandas()
  
      processed_col_a = [-1.5, 0]
      processed_col_b = [0, np.log(2)]
      expected_df = pd.DataFrame.from_dict(
          {"A": processed_col_a, "B": processed_col_b}
      )
  
      assert out_df.equals(expected_df)
  
      # yeo-johnson power=2
      transformer = PowerTransformer(["A", "B"], power=2)
      transformed = transformer.transform(ds)
      out_df = transformed.to_pandas()
      processed_col_a = [-np.log(2), 0]
      processed_col_b = [0, 1.5]
      expected_df = pd.DataFrame.from_dict(
          {"A": processed_col_a, "B": processed_col_b}
      )
  
      assert out_df.equals(expected_df)
  
      # box-cox
      col_a = [1, 2]
      col_b = [3, 4]
      in_df = pd.DataFrame.from_dict({"A": col_a, "B": col_b})
      ds = ray.data.from_pandas(in_df)
  
      # box-cox power=0
      transformer = PowerTransformer(
          ["A", "B"], power=0, method="box-cox"
      )
      transformed = transformer.transform(ds)
      out_df = transformed.to_pandas()
  
      processed_col_a = [0, np.log(2)]
      processed_col_b = [np.log(3), np.log(4)]
      expected_df = pd.DataFrame.from_dict(
          {"A": processed_col_a, "B": processed_col_b}
      )
  
      assert out_df.equals(expected_df)
  
      # box-cox power=2
      transformer = PowerTransformer(
          ["A", "B"], power=2, method="box-cox"
      )
      transformed = transformer.transform(ds)
      out_df = transformed.to_pandas()
      processed_col_a = [0, 1.5]
      processed_col_b = [4, 7.5]
      expected_df = pd.DataFrame.from_dict(
          {"A": processed_col_a, "B": processed_col_b}
      )
  
      assert out_df.equals(expected_df)
  
imports: import numpy
  import pandas
  import pytest
  import ray
  from ray.data.preprocessors import PowerTransformer
label_desc: Use image node_id 1 for calling a global function with example usage: test_power_transformer() without return types