code: def test_ondoubleclick(self, fopen):
      goto = fopen.return_value.gotoline = mock.Mock()
      self.cbt_F1.OnDoubleClick()
      fopen.assert_called()
      goto.assert_called()
      goto.assert_called_with(self.cbt_F1.obj.lineno)
  
imports: from idlelib import browser
  from test.support import requires
  import unittest
  from unittest import mock
  from idlelib.idle_test.mock_idle import Func
  from idlelib.util import py_extensions
  from collections import deque
  import os.path
  import pyclbr
  from tkinter import Tk
  from idlelib.tree import TreeNode
label_desc: Use image node_id 8 for calling the ChildBrowserTreeItemTest obj's underlying member method code with example usage: obj.test_ondoubleclick(fopen) without return types