code: def test_group_by(self):
      StratifiedSplit(
          self.data,
          fmt="UIR",
          group_by="user",
          test_size=0.4,
          verbose=True,
      )
      StratifiedSplit(
          self.data,
          fmt="UIR",
          group_by="item",
          test_size=0.4,
          verbose=True,
      )
  
      try:
          StratifiedSplit(
              self.data, fmt="UIR", group_by=None, verbose=True
          )
      except ValueError:
          assert True
  
file_path: cornac/tests/cornac/eval_methods/test_stratified_split.py
imports: import unittest
  import itertools
  import random
  from math import isclose
  from cornac.eval_methods import StratifiedSplit
  from cornac.data import Reader
  from cornac.models import MF
  from cornac.metrics import MAE, Recall
label_desc: Use image node_id 2 for calling the TestStratifiedSplit obj's underlying member method code with example usage: obj.test_group_by() without return types