unittest mock with __new__ function lead to TypeError
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stdlib
type-bug
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Description
Bug report
Bug description:
import unittest
from unittest.mock import patch
class Summary(object):
def __init__(self, path):
print("Summary init")
def __del__(self):
print("Summary del")
def get_summary(self):
print("get_summary")
class MockSummary:
def __init__(self, path):
print("Mock start")
def __del__(self):
print("Mock end")
def get_summary(self):
print("mock_get_summary")
class TestSummary(unittest.TestCase):
def setUp(self):
pass
def tearDown(self):
pass
def test_summary(self):
# 1 success case
summary1 = Summary('path')
summary1.get_summary()
# 2 mock case
mock = patch.object(Summary, '__new__', return_value=MockSummary('path'))
mock.start()
summary2 = Summary('path')
summary2.get_summary()
mock.stop()
# 3 fail case
summary3 = Summary('path')
summary3.get_summary()
if __name__ == '__main__':
unittest.main()
When run this python unittest file, it turns out with error:
Summary init
get_summary
Mock start
mock_get_summary
ESummary del
======================================================================
ERROR: test_summary (__main__.TestSummary.test_summary)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/admin/workspace/python/testSummaryAll.py", line 46, in test_summary
summary3 = Summary('path')
^^^^^^^^^^^^^^^
TypeError: object.__new__() takes exactly one argument (the type to instantiate)
----------------------------------------------------------------------
Ran 1 test in 0.001s
FAILED (errors=1)
Mock end
All the instance init after the mock stop will be failed.
CPython versions tested on:
3.11
Operating systems tested on:
Linux
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start with the supplied unittest reproduction and inspect unittest.mock.patch.object behavior when patching Summary.new. Reproduce the failure after mock.stop(), then trace how the original constructor behavior is restored. Done means instances can be created after the patch is stopped and the regression is covered by a test.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- python
- Domain
- testing-qa
- Issue type
- Bug
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 38/100