code: def test_json_serializable(self):
      payload = {"box_mode": BoxMode.XYWH_REL}
      try:
          json.dumps(payload)
      except Exception:
          self.fail("JSON serialization failed")
  
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 15 for calling the TestBoxMode obj's underlying member method code with example usage: obj.test_json_serializable() without return types