code: def __len__(self):
      return 10
  
file_path: chainercv/tests/chainer_experimental_tests/datasets_tests/sliceable_tests/test_transform_dataset.py
imports: import unittest
  from chainercv.chainer_experimental.datasets.sliceable import SliceableDataset
  from chainercv.chainer_experimental.datasets.sliceable import TransformDataset
  from chainercv.utils import testing
label_desc: Use image node_id 1 for calling the SampleDataset obj's underlying member method code with example usage: obj.__len__() and returns: int