code: def setUp(self):
      self.dataset = VOCBboxDataset(
          split=self.split,
          year=self.year,
          use_difficult=self.use_difficult,
          return_difficult=self.return_difficult,
      )
      self.n_out = 4 if self.return_difficult else 3
  
file_path: chainercv/tests/datasets_tests/voc_tests/test_voc_bbox_dataset.py
imports: import unittest
  import numpy
  from chainer import testing
  from chainer.testing import attr
  from chainer.testing import condition
  from chainercv.datasets import voc_bbox_label_names
  from chainercv.datasets import VOCBboxDataset
  from chainercv.utils import assert_is_bbox_dataset
label_desc: Use image node_id 1 for calling the TestVOCBboxDataset obj's underlying member method code with example usage: obj.setUp() without return types