code: def test_showtip_on_mouse_enter_no_delay(self):
      tooltip = Hovertip(self.button, "ToolTip text", hover_delay=None)
      self.addCleanup(tooltip.hidetip)
      tooltip.showtip = add_call_counting(tooltip.showtip)
      root.update()
      self.assertFalse(self.is_tipwindow_shown(tooltip))
      self.button.event_generate("<Enter>", x=0, y=0)
      root.update()
      self.assertTrue(self.is_tipwindow_shown(tooltip))
      self.assertGreater(len(tooltip.showtip.call_args_list), 0)
  
imports: from idlelib.tooltip import TooltipBase, Hovertip
  from test.support import requires
  from functools import wraps
  import time
  from tkinter import Button, Tk, Toplevel
  import unittest
label_desc: Use image node_id 6 for calling the HovertipTest obj's underlying member method code with example usage: obj.test_showtip_on_mouse_enter_no_delay() without return types