code: def test_keys(self):
      self.assertEqual(
          self.dataset.keys, ("item0", "item1", "item2", "item3")
      )
  
imports: import numpy
  import unittest
  from chainercv.chainer_experimental.datasets.sliceable import GetterDataset
  from chainercv.utils import testing
label_desc: Use image node_id 2 for calling the TestGetterDataset obj's underlying member method code with example usage: obj.test_keys() without return types