code: def transition(self, key, start, finish, **kwargs):
      self.observed_notifications.append(
          {"key": key, "start": start, "finish": finish}
      )
  
file_path: distributed/distributed/diagnostics/tests/test_worker_plugin.py
imports: from __future__ import annotations
  import asyncio
  import warnings
  import pytest
  from distributed import Worker, WorkerPlugin
  from distributed.protocol.pickle import dumps
  from distributed.utils_test import async_poll_for, gen_cluster, inc
label_desc: Use image node_id 4 for calling the MyPlugin obj's underlying member method code with example usage: obj.transition(key, start, finish) without return types