Mocking functions with decorators

mockingwithdecorators.py

class Foo(object):
    def __init__(self, a, b):
        self._a = a
        self._b = b

    @property
    def a(self):
        return self._a


def test_foo(monkeypatch):
    
    myFoo = Foo('alpha', 'beta')
    assert myFoo.a == 'alpha'
    
    def replacementA(self):
        return self._b
    
    # call the decorator explicitly on the function to be mocked
    propertyReplacementA = property(replacementA)
    
    monkeypatch.setattr(Foo, 'a', propertyReplacementA)

    assert myFoo.a == 'beta'