code: def test_merge(self):
      # load coco files to be combined
      coco_path1 = "tests/data/coco_utils/terrain1_coco.json"
      coco_path2 = "tests/data/coco_utils/terrain2_coco.json"
      coco_dict1 = load_json(coco_path1)
      self.assertEqual(len(coco_dict1["images"]), 1)
      self.assertEqual(len(coco_dict1["annotations"]), 7)
      self.assertEqual(len(coco_dict1["categories"]), 1)
  
      coco_dict2 = load_json(coco_path2)
      self.assertEqual(len(coco_dict2["images"]), 1)
      self.assertEqual(len(coco_dict2["annotations"]), 5)
      self.assertEqual(len(coco_dict2["categories"]), 1)
  
      # merge without desired_name2id
      merged_coco_dict = merge(coco_dict1, coco_dict2)
      self.assertEqual(len(merged_coco_dict["images"]), 2)
      self.assertEqual(len(merged_coco_dict["annotations"]), 7)
      self.assertEqual(len(merged_coco_dict["categories"]), 1)
  
      # merge with desired_name2id
      desired_name2id = {"human": 1, "car": 2, "big_vehicle": 3}
      merged_coco_dict = merge(coco_dict1, coco_dict2, desired_name2id)
      self.assertEqual(len(merged_coco_dict["images"]), 2)
      self.assertEqual(len(merged_coco_dict["annotations"]), 12)
      self.assertEqual(len(merged_coco_dict["categories"]), 3)
      self.assertEqual(
          merged_coco_dict["annotations"][6]["category_id"], 1
      )
      self.assertEqual(
          merged_coco_dict["annotations"][6]["image_id"], 1
      )
      self.assertEqual(merged_coco_dict["annotations"][6]["id"], 7)
      self.assertEqual(
          merged_coco_dict["annotations"][7]["category_id"], 2
      )
      self.assertEqual(
          merged_coco_dict["annotations"][7]["image_id"], 3
      )
      self.assertEqual(merged_coco_dict["annotations"][7]["id"], 9)
  
imports: import os
  import shutil
  import unittest
  from sahi.utils.coco import merge, update_categories
  from sahi.utils.file import load_json
label_desc: Use image node_id 13 for calling the TestCocoUtils obj's underlying member method code with example usage: obj.test_merge() without return types