code: def test_method(self):
      # test Results.method is same as calling function/class
      res = self.res
      x = res.model.exog
  
      def fun(params):
          return np.dot(x, params) ** 2
  
      nl = NonlinearDeltaCov(fun, res.params, res.cov_params())
      nlm = res._get_wald_nonlinear(fun)
      # margeff excludes constant, last parameter in this case
      assert_allclose(
          nlm.se_vectorized(), nlm.se_vectorized(), rtol=1e-12
      )
      assert_allclose(nlm.predicted(), nlm.predicted(), rtol=1e-12)
      df = res.df_resid
      t1 = nl.summary(use_t=True, df=df)
      t2 = nlm.summary(use_t=True, df=df)
      assert_equal(str(t1), str(t2))
  
file_path: statsmodels/statsmodels/stats/tests/test_deltacov.py
imports: import numpy
  from numpy.testing import assert_allclose, assert_equal
  from statsmodels.regression.linear_model import OLS
  from statsmodels.stats._delta_method import NonlinearDeltaCov
label_desc: Use image node_id 2 for calling the TestDeltacovOLS obj's underlying member method code with example usage: obj.test_method() and returns: unknown