code: def test_basic(self):
      dataset = ConcatenatedDataset(self.dataset, self.dataset)
      self.assertIsInstance(dataset, SliceableDataset)
      self.assertEqual(len(dataset), len(self.dataset) * 2)
      self.assertEqual(dataset.keys, ("item0", "item1", "item2"))
      self.assertEqual(dataset[1], ("item0(1)", "item1(1)", "item2(1)"))
      self.assertEqual(
          dataset[11], ("item0(1)", "item1(1)", "item2(1)")
      )
  
file_path: chainercv/tests/chainer_experimental_tests/datasets_tests/sliceable_tests/test_concatenated_dataset.py
imports: import unittest
  from chainer import testing
  from chainercv.chainer_experimental.datasets.sliceable import ConcatenatedDataset
  from chainercv.chainer_experimental.datasets.sliceable import SliceableDataset
label_desc: Use image node_id 2 for calling the TestConcatenatedDataset obj's underlying member method code with example usage: obj.test_basic() without return types