code: def test_empty_cat(self):
      x = Boxes.cat([])
      self.assertTrue(x.tensor.shape, (0, 4))
  
imports: import json
  import math
  import numpy
  import unittest
  import torch
  from detectron2.structures import Boxes, BoxMode, pairwise_ioa, pairwise_iou
  from detectron2.utils.testing import reload_script_model
label_desc: Use image node_id 1 for calling the TestBoxes obj's underlying member method code with example usage: obj.test_empty_cat() without return types