code: def test_fit():
      model = BaseUncertaintyModel(uncertainty_dict={})
      model.fit(train_df=pd.DataFrame({}))
      assert model.train_df is not None
  
imports: import pandas
  import pytest
  from greykite.sklearn.uncertainty.base_uncertainty_model import BaseUncertaintyModel
  from greykite.sklearn.uncertainty.uncertainty_methods import UncertaintyMethodEnum
label_desc: Use image node_id 4 for calling a global function with example usage: test_fit() without return types