code: def test_run_undefined_event_on_collection(self):
      collection = plugins.PluginCollection()
      self.assertEqual(
          collection.on_page_markdown(
              "page markdown", page=None, config={}, files=[]
          ),
          "page markdown",
      )
  
imports: from __future__ import annotations
  import os
  import unittest
  from typing import TYPE_CHECKING, Optional
  from mkdocs import plugins
  from mkdocs.commands import build
  from mkdocs.config import base
  from mkdocs.config import config_options
  from mkdocs.config.base import ValidationError
  from mkdocs.exceptions import Abort, BuildError, PluginError
  from mkdocs.tests.base import load_config, tempdir
label_desc: Use image node_id 10 for calling the TestPluginCollection obj's underlying member method code with example usage: obj.test_run_undefined_event_on_collection() without return types