code: def test_no_pos_ratio(self):
      dataset = SiameseDataset(self.dataset_0, self.dataset_1)
      for i in range(10):
          example = dataset[i]
          self._check_example(example)
      self.assertEqual(len(dataset), N)
  
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 3 for calling the TestSiameseDataset obj's underlying member method code with example usage: obj.test_no_pos_ratio() without return types