unittest.mock.patch() cannot properly mock methods

GitHub fields:

assignee = None
closed_at = None
created_at = <Date 2020-12-03.14:41:06.568>
labels = ['3.8', '3.7', 'library', '3.9', '3.10']
title = 'unittest.mock.patch() cannot properly mock methods'
updated_at = <Date 2020-12-16.17:12:39.719>
user = 'https://github.com/CendioOssman'

bugs.python.org fields:

activity = <Date 2020-12-16.17:12:39.719>
actor = 'mariocj89'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation = <Date 2020-12-03.14:41:06.568>
creator = 'CendioOssman'
dependencies = []
files = []
hgrepos = []
issue_num = 42556
keywords = []
message_count = 2.0
messages = ['382415', '383189']
nosy_count = 5.0
nosy_names = ['cjw296', 'michael.foord', 'mariocj89', 'xtreak', 'CendioOssman']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = None
url = 'https://bugs.python.org/issue42556'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8', 'Python 3.9', 'Python 3.10']