code: def test_get_train_test_sets_next_fold(self):
      for n in range(self.cv.n_folds):
          self.cv._get_train_test()
          self.assertEqual(self.cv.current_fold, n)
          self.assertSequenceEqual(
              self.cv.train_set.matrix.shape, (8, 8)
          )
          self.cv._next_fold()
  
file_path: cornac/tests/cornac/eval_methods/test_cross_validation.py
imports: import unittest
  import numpy
  from cornac.eval_methods import CrossValidation
  from cornac.data import Reader
label_desc: Use image node_id 4 for calling the TestCrossValidation obj's underlying member method code with example usage: obj.test_get_train_test_sets_next_fold() without return types