Issue #11816: Add missing test helper

This is why I should really use hg import rather than patch,
but old habits die hard...
Fix uninitialized value in charmap_decode_mapping()
Issue 17920:  Fix-up terminology in the set documentation
merge
#17871: fix unittest.TextTestRunner signature in the docs.  Patch by Yogesh Chaudhari.
#17871: merge with 3.3.
#17714: document that the base64 codec adds a trailing newline.
#17714: merge with 3.3.
Skip failing test pending investigation.
Fix os.__all__ to is passes test___all__
Correction for 4f82b6cfee46.
Fix a compiler warning: in and out are unused in _Py_char2wchar() if
HAVE_MBRTOWC is not defined
audioop: explicit cast to fix a compiler warning
Fix a compiler warning: use unsigned int type instead of enum PyUnicode_Kind to
compare two Unicode kinds
zlib: Explicit cast to fix a compiler warning