code: def test_strata(self):
      for n_strata in range(2, 5):
          self.test_propensity(n_strata)
          self.test_stratified_split(n_strata)
  
file_path: cornac/tests/cornac/eval_methods/test_propensity_stratified_evaluation.py
imports: import unittest
  import numpy
  import cornac
  from cornac.data import Reader
  from cornac.eval_methods import PropensityStratifiedEvaluation
  from cornac.models import MF
  from cornac.metrics import MAE, AUC
label_desc: Use image node_id 4 for calling the TestPropensityStratifiedEvaluation obj's underlying member method code with example usage: obj.test_strata() without return types