test_venv.TestEnsurePip fails mysteriously when /tmp is too small

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2016-07-16.02:09:05.361>
labels = ['type-bug']
title = 'test_venv.TestEnsurePip fails mysteriously when /tmp is too small'
updated_at = <Date 2018-09-25.14:54:10.797>
user = 'https://github.com/bitdancer'

bugs.python.org fields:

activity = <Date 2018-09-25.14:54:10.797>
actor = 'xtreak'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = []
creation = <Date 2016-07-16.02:09:05.361>
creator = 'r.david.murray'
dependencies = []
files = []
hgrepos = []
issue_num = 27526
keywords = []
message_count = 1.0
messages = ['270532']
nosy_count = 3.0
nosy_names = ['r.david.murray', 'dstufft', 'xtreak']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue27526'
versions = []