code: def __init__(self, dashboard_head):
      super().__init__(dashboard_head)
      self._notified_agents = {}
      DataSource.agents.signal.append(self._update_notified_agents)
  
file_path: ray/python/ray/dashboard/modules/tests/test_head.py
imports: import logging
  import time
  import aiohttp.web
  import ray.dashboard.modules.tests.test_consts
  import ray.dashboard.modules.tests.test_utils
  import ray.dashboard.optional_utils
  import ray.dashboard.utils
  from ray._private.ray_constants import env_bool
  from ray.dashboard.datacenter import DataSource
label_desc: Use image node_id 1 to create a new TestHead object from inherited base classes: dashboard_utils with example: obj = TestHead(dashboard_head)