code: def test_return_type_dataframe(df):
      X, y = df[["a", "b", "c", "d"]], df[["e"]]
      tf = PatsyTransformer("a + b - 1", return_type="dataframe")
      df_fit_transformed = tf.fit(X, y).transform(X)
      assert isinstance(df_fit_transformed, pd.DataFrame)
  
file_path: scikit-lego/tests/test_preprocessing/test_patsy_transformer.py
imports: import numpy
  import pandas
  import pytest
  from sklearn.linear_model import LogisticRegression
  from sklearn.pipeline import Pipeline
  from sklearn.preprocessing import StandardScaler
  from sklego.preprocessing import PatsyTransformer
label_desc: Use image node_id 3 for calling a global function with example usage: test_return_type_dataframe(df) without return types