My experiments and some web postings indicate that if a tkinter class has a master or parent option, it may not really be an option, regardless of what our docs imply. If tkinter.Tk is called either directly or indirectly, the graphics system is initiated and something is displayed. This appears to includes the seemingly non-graphics Variable (Var) classes such as IntVar (#18131). I started idle_lib/mock_tk.py as part of #18130. This will allow non-gui unit testing of any method whose tkinter use is limited to Vars and message boxes.