For the record, a typical instance of this failure will look like this:

$ /usr/local/bin/python3.4 -m test -w -uall -j2
== CPython 3.4.2 (v3.4.2:ab2c023a9432, Oct 5 2014, 20:42:22) [GCC 4.2.1 (Apple Inc. build 5666) (dot 3)]
==   Darwin-14.0.0-x86_64-i386-64bit little-endian
==   hash algorithm: siphash24 64bit
==   /private/var/folders/fm/9wjgctqx61n796zt88qmmnxc0000gq/T/test_python_89951
Testing with flags: sys.flags(debug=0, inspect=0, interactive=0, optimize=0, dont_write_bytecode=0, no_user_site=0, no_site=0, ignore_environment=0, verbose=0, bytes_warning=0, quiet=0, hash_randomization=1, isolated=0)
[...] test_ttk_guionly
Fatal Python error: Segmentation fault

Current thread 0x00007fff747dd300 (most recent call first):
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/tkinter/__init__.py", line 496 in wait_visibility
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/tkinter/test/test_ttk/test_extensions.py", line 121 in test_horizontal_range
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/case.py", line 577 in run
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/case.py", line 625 in __call__
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/suite.py", line 125 in run
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/suite.py", line 87 in __call__
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/suite.py", line 125 in run
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/suite.py", line 87 in __call__
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/unittest/runner.py", line 168 in run
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/support/__init__.py", line 1750 in _run_suite
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/support/__init__.py", line 1784 in run_unittest
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/test_ttk_guionly.py", line 34 in test_main
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 1280 in runtest_inner
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 978 in runtest
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 532 in main
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 1564 in main_in_temp_cwd
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 1589 in <module>
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 85 in _run_code
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 170 in _run_module_as_main
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 170, in _run_module_as_main
    "__main__", mod_spec)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/__main__.py", line 3, in <module>
    regrtest.main_in_temp_cwd()
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 1564, in main_in_temp_cwd
    main()
  File "/Library/Frameworks/Python.framework/Versions/3.4/lib/python3.4/test/regrtest.py", line 738, in main
    raise Exception("Child error on {}: {}".format(test, result[1]))
Exception: Child error on test_ttk_guionly: Exit code -11

and the system crash report will look something like this:

[...]
Process:               Python [89955]
Path:                  /Library/Frameworks/Python.framework/Versions/3.4/Resources/Python.app/Contents/MacOS/Python
Identifier:            org.python.python
Version:               3.4.2 (3.4.2)
Code Type:             X86-64 (Native)
Parent Process:        Python [89951]
Responsible:           iTerm [64155]
User ID:               503

Date/Time:             2014-10-30 12:47:52.051 -0700
OS Version:            Mac OS X 10.10 (14A389)
Report Version:        11
Anonymous UUID:        CFED52E3-698C-835B-D61C-F4B1F18D2CB6


Time Awake Since Boot: 600000 seconds

Crashed Thread:        0  Dispatch queue: com.apple.main-thread

Exception Type:        EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       KERN_INVALID_ADDRESS at 0x0000000000000170

VM Regions Near 0x170:
--> 
    __TEXT                 0000000100000000-0000000100001000 [    4K] r-x/rwx SM=COW  /Library/Frameworks/Python.framework/Versions/3.4.2_10_6/Resources/Python.app/Contents/MacOS/Python

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libsystem_kernel.dylib        	0x00007fff90cadc7e __kill + 10
1   ???                           	000000000000000000 0 + 0
2   Tcl                           	0x0000000101810430 Tcl_GetCommandInfo + 21
3   Tk                            	0x00000001019c0ae0 OappHandler + 55
4   com.apple.AE                  	0x00007fff88d6899c aeDispatchAppleEvent(AEDesc const*, AEDesc*, unsigned int, unsigned char*) + 531
5   com.apple.AE                  	0x00007fff88d68719 dispatchEventAndSendReply(AEDesc const*, AEDesc*) + 31
6   com.apple.AE                  	0x00007fff88d68623 aeProcessAppleEvent + 295
7   com.apple.HIToolbox           	0x00007fff8aa6e37e AEProcessAppleEvent + 56
8   com.apple.AppKit              	0x00007fff900d9ec6 _DPSNextEvent + 2665
9   com.apple.AppKit              	0x00007fff900d8fd0 -[NSApplication nextEventMatchingMask:untilDate:inMode:dequeue:] + 194
10  Tk                            	0x00000001019c9bc0 -[TKApplication(TKNotify) nextEventMatchingMask:untilDate:inMode:dequeue:] + 169
11  Tk                            	0x00000001019ca194 TkMacOSXEventsSetupProc + 209
12  Tcl                           	0x0000000101876991 Tcl_DoOneEvent + 220
13  Tk                            	0x000000010191793f Tk_TkwaitObjCmd + 398
14  Tcl                           	0x000000010181085a TclEvalObjvInternal + 773
15  Tcl                           	0x0000000101811a2d Tcl_EvalObjv + 66
16  _tkinter.so                   	0x000000010163cabe Tkapp_Call + 190
17  org.python.python             	0x00000001000e4745 PyEval_EvalFrameEx + 29589
[...]