New submission from melwitt <[email protected]>:
When async magic method support was added to unittest.mock.Mock to address
issue #26467, it introduced a getattr call [1] that causes class properties to
be called when the class is used as a mock spec.
This caused a problem for a test in my project when running with Python 3.8
where previously the test worked OK with Python 3.6.
The test aims to verify that a class instance is not created if the called code
path does not access the class property and thus the class will not create a
heavy object unless it's needed (lazy create on access via @property).
As of Python 3.8, the @property is always called and is called by the mock spec
process itself, even though the code path being tested does not access the
class @property.
Here is a code snippet that illustrates the @property calling from the mock
spec alone:
class SomethingElse(object):
def __init__(self):
self._instance = None
@property
def instance(self):
if not self._instance:
self._instance = 'object'
...
def test_property_not_called_with_spec_mock(self):
obj = SomethingElse()
self.assertIsNone(obj._instance)
mock = Mock(spec=obj)
self.assertIsNone(obj._instance)
$ ./python -m unittest -v
unittest.test.testmock.testmock.MockTest.test_property_not_called_with_spec_mock
test_property_not_called_with_spec_mock
(unittest.test.testmock.testmock.MockTest) ... FAIL
======================================================================
FAIL: test_property_not_called_with_spec_mock
(unittest.test.testmock.testmock.MockTest)
----------------------------------------------------------------------
Traceback (most recent call last):
File "/home/vagrant/cpython/Lib/unittest/test/testmock/testmock.py", line
2173, in test_property_not_called_with_spec_mock
self.assertIsNone(obj._instance)
AssertionError: 'object' is not None
[1]
https://github.com/python/cpython/blob/fb2718720346c8c7a0ad2d7477f20e9a5524ea0c/Lib/unittest/mock.py#L492
----------
components: Library (Lib)
messages: 376757
nosy: melwitt
priority: normal
severity: normal
status: open
title: unittest.mock spec calls class properties
type: behavior
versions: Python 3.8
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Python tracker <[email protected]>
<https://bugs.python.org/issue41768>
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