python - 断言在特定实例上调用了 PropertyMock

Question

我已经成功地用 PropertyMock 模拟了一个属性，但我不知道如何检查类的哪个实例调用了该属性。我如何断言该属性是在一个对象上调用的，而不是在另一个对象上调用的？

这是我想断言 foo1.is_big 的示例被调用，和 foo2.is_big不是:

from mock import PropertyMock, patch


class Foo(object):
    def __init__(self, size):
        self.size = size

    @property
    def is_big(self):
        return self.size > 5

f = Foo(3)
g = Foo(10)
assert not f.is_big
assert g.is_big

with patch('__main__.Foo.is_big', new_callable=PropertyMock) as mock_is_big:
    mock_is_big.return_value = True
    foo1 = Foo(4)
    foo2 = Foo(9)

    should_pass = False
    if should_pass:
        is_big = foo1.is_big
    else:
        is_big = foo2.is_big
    assert is_big
    # How can I make this pass when should_pass is True, and fail otherwise?
    mock_is_big.assert_called_once_with()

print('Done.')

当前代码将在调用其中任何一个时通过。

Answer 1

也许有更好的方法，但我通过创建 PropertyMock 的子类让它工作。它将被调用的实例记录为模拟调用的参数之一。

from mock import PropertyMock, patch


class Foo(object):
    def __init__(self, size):
        self.size = size

    @property
    def is_big(self):
        return self.size > 5


class PropertyInstanceMock(PropertyMock):
    """Like PropertyMock, but records the instance that was called."""

    def __get__(self, obj, obj_type):
        return self(obj)

    def __set__(self, obj, val):
        self(obj, val)


with patch("__main__.Foo.is_big", new_callable=PropertyInstanceMock) as mock_is_big:
    mock_is_big.return_value = True
    foo1 = Foo(4)
    foo2 = Foo(9)

    should_pass = False
    if should_pass:
        is_big = foo1.is_big
    else:
        is_big = foo2.is_big
    assert is_big
    # Now this passes when should_pass is True, and fails otherwise.
    mock_is_big.assert_called_once_with(foo1)

print("Done.")