Decompose TESTFN_UNICODE on Mac OS X

Lib/test/support.py

@@ -379,6 +379,12 @@ TESTFN = "{}_{}_tmp".format(TESTFN, os.getpid())
 
 # TESTFN_UNICODE is a non-ascii filename
 TESTFN_UNICODE = TESTFN + "-\xe0\xf2\u0258\u0141\u011f"
+if sys.platform == 'darwin':
+    # In Mac OS X's VFS API file names are, by definition, canonically
+    # decomposed Unicode, encoded using UTF-8. See QA1173:
+    # http://developer.apple.com/mac/library/qa/qa2001/qa1173.html
+    import unicodedata
+    TESTFN_UNICODE = unicodedata.normalize('NFD', TESTFN_UNICODE)
 TESTFN_ENCODING = sys.getfilesystemencoding()
 
 # TESTFN_UNENCODABLE is a filename (str type) that should *not* be able to be