code: def test_std(self):
      # Use vardef=wgt option in SAS to match
      std = self.descriptive.std
      assert_allclose(std, self.std, rtol=1e-4)
  
imports: import numpy
  from scipy import stats
  import pandas
  from numpy.testing import assert_, assert_almost_equal, assert_allclose
  from statsmodels.stats.weightstats import DescrStatsW, CompareMeans, ttest_ind, ztest, zconfint
  from statsmodels.tools.testing import Holder
label_desc: Use image node_id 6 for calling the CheckExternalMixin obj's underlying member method code with example usage: obj.test_std() without return types