code: def test_df(self):
      # TODO: make into attributes
      assert_equal(
          self.res_ps.df_model(), self.res2.df_model + 1
      )  # with const
      assert_equal(
          self.res_ps.df_fit(), self.res2.df_model + 1
      )  # alias
      assert_equal(self.res_ps.df_resid(), self.res2.df_resid)
  
imports: import numpy
  from numpy.testing import assert_almost_equal, assert_equal
  from statsmodels.sandbox.nonparametric import smoothers
  from statsmodels.regression.linear_model import OLS, WLS
label_desc: Use image node_id 3 for calling the CheckSmoother obj's underlying member method code with example usage: obj.test_df() without return types