Currently Tkinter tests are splitted on four tests: test_tcl, test_tk, test_ttk_textonly, test_ttk_guionly. Ttk tests are separated because ttk is optional on Tk 8.4 and because ttk is separate large part of Tkinter. test_tcl and test_ttk_textonly are separated because they don't require GUI. On headless computer test_tk and test_ttk_guionly are reported as skipped at all, but test_tcl and test_ttk_textonly should run. It would be good to preserve this splitting and even improve it (test_variables does not require GUI and can be moved to test_tcl package).

Tkinter tests are still incomplete and needs many test. To avoid obstacles for backporting new tests it is worth to apply these changes to all maintained branches.