> Since this buildbot is set up in an environment where it is
> "running headless", that is to say the tests are run under
> a username that is not logged in to the window server, we should
> not be trying to run GUI tests there, in particular Tkinter tests.

If I run test_ttk_guionly in SSH, the process abort. gdb trace:
-----------------------
...
kCGErrorRangeCheck : Window Server communications from outside of session allowed for root and console user only
INIT_Processeses(), could not establish the default connection to the WindowServer.
Program received signal SIGABRT, Aborted.
0x9003d66c in kill ()
(gdb) where
#0  0x9003d66c in kill ()
#1  0x9010e8cf in raise ()
#2  0x9010d422 in abort ()
#3  0x917d7dad in RegisterProcess ()
#4  0x917d7b55 in INIT_Processes ()
#5  0x918080b6 in ProcessManagerLazyInitialization ()
#6  0x917d7aa6 in GetCurrentProcess ()
#7  0x92dd5ef9 in GetSystemUIMode ()
#8  0x92dd5e86 in IsMenuBarVisible ()
#9  0x92e2af35 in GetAvailableWindowPositioningBounds ()
#10 0x0b0a7a31 in TkMacOSXDisplayChanged ()
#11 0x0b0a7bee in TkpOpenDisplay ()
#12 0x0b02ace6 in CreateTopLevelWindow ()
#13 0x0b02b0dd in TkCreateMainWindow ()
#14 0x0b035115 in CreateFrame ()
#15 0x0b035544 in TkCreateFrame ()
#16 0x0b02c564 in Initialize ()
#17 0x010d2789 in Tcl_AppInit (interp=0x12c6010) at /Users/vstinner/cpython/Modules/tkappinit.c:106
#18 0x010cc000 in Tkapp_New (screenName=0x0, className=0x10d2e8c "Tk", interactive=0, wantobjects=0, wantTk=1, sync=0, use=0x0) at /Users/vstinner/cpython/Modules/_tkinter.c:724
#19 0x010d1dcd in Tkinter_Create (self=0x1275838, args=0x517038) at /Users/vstinner/cpython/Modules/_tkinter.c:2938
#20 0x00060241 in PyCFunction_Call (func=0x106c338, arg=0x517038, kw=0x0) at Objects/methodobject.c:81
#21 0x0008de54 in call_function (pp_stack=0xbffff164, oparg=0) at Python/ceval.c:3957
#22 0x00087f81 in PyEval_EvalFrameEx (f=0x1255d28, throwflag=0) at Python/ceval.c:2663
#23 0x0008bf7d in PyEval_EvalCodeEx (_co=0x7a7df8, globals=0x705428, locals=0x705428, args=0x0, argcount=0, kws=0x0, kwcount=0, defs=0x0, defcount=0, kwdefs=0x0, closure=0x0) at Python/ceval.c:3393
#24 0x00079362 in PyEval_EvalCode (co=0x7a7df8, globals=0x705428, locals=0x705428) at Python/ceval.c:767
#25 0x000e1a9f in run_mod (mod=0x18bdba0, filename=0x1caac8 "<string>", globals=0x705428, locals=0x705428, flags=0xbffffa34, arena=0x1101470) at Python/pythonrun.c:1793
#26 0x000e17a4 in PyRun_StringFlags (str=0x125f520 "import _tkinter; c=_tkinter.create(); print(\"a\")\n", start=257, globals=0x705428, locals=0x705428, flags=0xbffffa34) at Python/pythonrun.c:1727
#27 0x000dfe61 in PyRun_SimpleStringFlags (command=0x125f520 "import _tkinter; c=_tkinter.create(); print(\"a\")\n", flags=0xbffffa34) at Python/pythonrun.c:1300
#28 0x0000714c in run_command (command=0x11010e0, cf=0xbffffa34) at Modules/main.c:260
#29 0x00007f4a in Py_Main (argc=3, argv=0x514028) at Modules/main.c:634
#30 0x000024d3 in main (argc=3, argv=0xbffffb6c) at ./Modules/python.c:59
-----------------------

The best would be to fix _tkinter to catch Tk error, but I agree, in a first time we may just try to detect that we cannot create GUI objects. For example, test if the DISPLAY environment variable is present.

"PPC Tiger 3.x": test_ttk_guionly crashs sometimes, the variable is not set.

"AMD64 Leopard 3.x": test_tcl, test_tk, test_ttk_guionly and test_ttk_textonly are skipped; the variable is set (e.g. DISPLAY=/tmp/launch-lDC93s/:0).

"AMD64 Snow Leopard 2 3.x": test_ttk_guionly pass, DISPLAY var is set (e.g. DISPLAY=/tmp/launch-cuyZPv/org.x:0).

Attached requires_tkinter.patch file adds the check for test_tk and test_ttk_guionly.