unittest subTest does not call addFailure

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2017-01-04.12:57:35.198>
labels = ['3.7', 'type-bug', 'library']
title = 'unittest subTest does not call addFailure'
updated_at = <Date 2017-01-23.21:12:35.391>
user = 'https://bugs.python.org/kristall'

bugs.python.org fields:

activity = <Date 2017-01-23.21:12:35.391>
actor = 'martin.panter'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2017-01-04.12:57:35.198>
creator = 'kristall'
dependencies = []
files = []
hgrepos = []
issue_num = 29152
keywords = []
message_count = 4.0
messages = ['284635', '284691', '286085', '286117']
nosy_count = 4.0
nosy_names = ['pitrou', 'kristall', 'berker.peksag', 'martin.panter']
pr_nums = []
priority = 'normal'
resolution = None
stage = 'test needed'
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue29152'
versions = ['Python 3.5', 'Python 3.6', 'Python 3.7']