code: def test_cat_keypoints(self):
      keypoints1 = Keypoints(torch.rand(2, 21, 3))
      keypoints2 = Keypoints(torch.rand(4, 21, 3))
  
      cat_keypoints = keypoints1.cat([keypoints1, keypoints2])
      self.assertTrue(
          torch.all(
              cat_keypoints.tensor[:2] == keypoints1.tensor
          ).item()
      )
      self.assertTrue(
          torch.all(
              cat_keypoints.tensor[2:] == keypoints2.tensor
          ).item()
      )
  
imports: import unittest
  import torch
  from detectron2.structures.keypoints import Keypoints
label_desc: Use image node_id 1 for calling the TestKeypoints obj's underlying member method code with example usage: obj.test_cat_keypoints() without return types