code: def test_imputation(self):
      default_schema = "continuous"
      new_schema = validate_schema(
          nodes=["new"], schema=None, default_type=default_schema
      )
      assert new_schema["new"] == default_schema
  
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 4 for calling the TestValidateSchema obj's underlying member method code with example usage: obj.test_imputation() without return types