code: def test_automatically_finds_variables(df_vartypes):
      # test case 1: automatically select variables
      transformer = BoxCoxTransformer(variables=None)
      X = transformer.fit_transform(df_vartypes)
  
      # expected output
      transf_df = df_vartypes.copy()
      transf_df["Age"] = [9.78731, 10.1666, 9.40189, 9.0099]
      transf_df["Marks"] = [-0.101687, -0.207092, -0.316843, -0.431788]
  
      # test init params
      assert transformer.variables is None
      # test fit attr
      assert transformer.variables_ == ["Age", "Marks"]
      assert transformer.n_features_in_ == 5
      # test transform output
      pd.testing.assert_frame_equal(X, transf_df)
  
      # test inverse_transform
      Xit = transformer.inverse_transform(X)
  
      # convert numbers to original format.
      Xit["Age"] = Xit["Age"].round().astype("int64")
      Xit["Marks"] = Xit["Marks"].round(1)
  
      # test
      pd.testing.assert_frame_equal(Xit, df_vartypes)
  
file_path: feature_engine/tests/test_transformation/test_boxcox_transformer.py
imports: import pandas
  import pytest
  from sklearn.exceptions import NotFittedError
  from feature_engine.transformation import BoxCoxTransformer
label_desc: Use image node_id 1 for calling a global function with example usage: test_automatically_finds_variables(df_vartypes) without return types