code: def fit(self):
      return self
  
file_path: feature_engine/tests/test_encoding/test_base_encoder.py
imports: import numpy
  import pandas
  import pytest
  from feature_engine.encoding.base_encoder import CategoricalInitMixin, CategoricalMethodsMixin
label_desc: Use image node_id 2 for calling the MockClass obj's underlying member method code with example usage: obj.fit() and returns: self