code: def test_pos_ratio_equals_0(self):
      if self.neg_exist:
          dataset = SiameseDataset(self.dataset_0, self.dataset_1, 0)
  
          for i in range(10):
              example = dataset[i]
              self._check_example(example)
              if self.neg_exist:
                  self.assertNotEqual(example[1], example[3])
          self.assertEqual(len(dataset), N)
      else:
          with self.assertRaises(ValueError):
              dataset = SiameseDataset(
                  self.dataset_0, self.dataset_1, 0
              )
  
file_path: chainercv/tests/datasets_tests/test_siamese_dataset.py
imports: import unittest
  import numpy
  from chainer import testing
  from chainer.datasets import TupleDataset
  from chainercv.datasets import SiameseDataset
  from chainercv.utils.testing.assertions.assert_is_image import assert_is_image
label_desc: Use image node_id 5 for calling the TestSiameseDataset obj's underlying member method code with example usage: obj.test_pos_ratio_equals_0() without return types