code: def test_set_dataset_classes(self):
      assert isinstance(self.dataset.metainfo, dict)
      assert len(self.dataset.metainfo["classes"]) == 40
  
imports: from unittest import TestCase
  from mmdet.datasets import YouTubeVISDataset
label_desc: Use image node_id 2 for calling the TestYouTubeVISDataset obj's underlying member method code with example usage: obj.test_set_dataset_classes() without return types