What should the error message in the exception raised by assertTrue and assertFalse be?

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2019-11-05.21:16:18.934>
labels = ['type-feature', 'library', '3.9']
title = 'What should the error message in the exception raised by assertTrue and assertFalse be?'
updated_at = <Date 2019-12-06.11:51:47.142>
user = 'https://github.com/michael-karotsieris'

bugs.python.org fields:

activity = <Date 2019-12-06.11:51:47.142>
actor = 'steven.daprano'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2019-11-05.21:16:18.934>
creator = 'mkarotsieris'
dependencies = []
files = []
hgrepos = []
issue_num = 38706
keywords = ['patch']
message_count = 17.0
messages = ['356065', '356067', '356081', '356082', '356083', '356103', '356104', '356105', '356114', '356120', '356124', '356126', '356179', '356206', '356208', '356211', '357911']
nosy_count = 12.0
nosy_names = ['terry.reedy', 'mark.dickinson', 'rbcollins', 'ezio.melotti', 'steven.daprano', 'r.david.murray', 'michael.foord', 'petr.viktorin', 'serhiy.storchaka', 'ammar2', 'brandtbucher', 'mkarotsieris']
pr_nums = ['17049', '17073']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue38706'
versions = ['Python 3.9']