code: def test_df(self):
      # not used yet, copied from PolySmoother tests
      assert_equal(self.res_ps.df_model(), self.res2.df_model)
      assert_equal(self.res_ps.df_fit(), self.res2.df_model)  # alias
      assert_equal(self.res_ps.df_resid(), self.res2.df_resid)
  
imports: from statsmodels.compat.python import lrange
  import numpy
  from numpy.testing import assert_almost_equal, assert_equal
  from scipy import stats
  import pytest
  from statsmodels.sandbox.gam import AdditiveModel
  from statsmodels.sandbox.gam import Model
  from statsmodels.genmod.families import family, links
  from statsmodels.genmod.generalized_linear_model import GLM
  from statsmodels.regression.linear_model import OLS
label_desc: Use image node_id 4 for calling the CheckAM obj's underlying member method code with example usage: obj.test_df() without return types