code: def test_cdf_ppf_roundtrip(self):
      # round trip
      probs = np.linspace(0.001, 0.999, 6)
      ppf = self.dist2.ppf(probs)
      cdf = self.dist2.cdf(ppf)
      assert_allclose(cdf, probs, rtol=1e-6)
      sf = self.dist2.sf(ppf)
      assert_allclose(sf, 1 - probs, rtol=1e-6)
  
file_path: statsmodels/statsmodels/sandbox/distributions/tests/test_norm_expan.py
imports: import pytest
  import numpy
  from scipy import stats
  from numpy.testing import assert_allclose, assert_array_less
  from statsmodels.sandbox.distributions.extras import NormExpan_gen
label_desc: Use image node_id 2 for calling the CheckDistribution obj's underlying member method code with example usage: obj.test_cdf_ppf_roundtrip() without return types