code: def test_get_feature_index(self, mapper):
      assert mapper.get_feature_index("B") == 0
      assert mapper.get_feature_index("C_0") == 3
      # The 0 variable will be converted to a string when we
      assert mapper.get_feature_index("0_0") == 8
  
imports: from collections import OrderedDict
  import pytest
  from causalnex.structure import StructureModel
  from causalnex.structure.categorical_variable_mapper import VariableFeatureMapper, validate_schema
label_desc: Use image node_id 2 for calling the TestVariableFeatureMapper obj's underlying member method code with example usage: obj.test_get_feature_index(mapper) without return types