Message 376757 - Python tracker (original) (raw)
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