code: def test_init(self):
      fake_json_file = osp.join(self.tmp_dir.name, "fake_data.json")
      self._create_dummy_coco_json(fake_json_file)
      with self.assertRaisesRegex(KeyError, "metric should be one of"):
          CocoMetric(ann_file=fake_json_file, metric="unknown")
  
imports: import os.path
  import tempfile
  from unittest import TestCase
  import numpy
  import pycocotools.mask
  import torch
  from mmengine.fileio import dump
  from mmdet.evaluation import CocoMetric
label_desc: Use image node_id 5 for calling the TestCocoMetric obj's underlying member method code with example usage: obj.test_init() without return types