I'm asking how to mock a class property in a unit test using Python 3. I've tried the following, which makes sense for me following the docs, but it doesn't work:
foo.py:
class Foo():
@property
def bar(self):
return 'foobar'
def test_foo_bar(mocker):
foo = Foo()
mocker.patch.object(foo, 'bar', new_callable=mocker.PropertyMock)
print(foo.bar)
I've installed pytest and pytest_mock and run the test like this:
pytest foo.py
I got the following error:
> setattr(self.target, self.attribute, new_attr)
E AttributeError: can't set attribute
/usr/lib/python3.5/unittest/mock.py:1312: AttributeError
My expectation would be that the test runs without errors.
The property mechanism relies on the property attribute being defined on the object's class. You can't create a "property like" method or attribute on a single instance of a class (for a better understanding, read about Python's descriptor protocol)
Therefore you have to apply the patch to your class - you can use the with statement so that the class is properly restored after your test:
def test_foo_bar(mock):
foo = Foo()
with mock.patch(__name__ + "Foo.bar", new=mocker.PropertyMock)
print(foo.bar)