Message376757
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 |
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Date |
User |
Action |
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2020-09-12 01:10:24 | melwitt | set | recipients:
+ melwitt |
2020-09-12 01:10:24 | melwitt | set | messageid: <1599873024.24.0.929930382889.issue41768@roundup.psfhosted.org> |
2020-09-12 01:10:24 | melwitt | link | issue41768 messages |
2020-09-12 01:10:23 | melwitt | create | |
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