如何用模拟模拟只读属性? [英] How to mock a readonly property with mock?

问题描述

如何使用 mock 模拟只读属性?

How do you mock a readonly property with mock?

我尝试过:

setattr(obj.__class__, 'property_to_be_mocked', mock.Mock())

但是问题在于它随后适用于该类的所有实例...这破坏了我的测试.

but the issue is that it then applies to all instances of the class... which breaks my tests.

您还有其他想法吗?我不想模拟整个对象，仅模拟这个特定属性.

Do you have any other idea? I don't want to mock the full object, only this specific property.

推荐答案

我认为更好的方法是将属性模拟为PropertyMock，而不是直接模拟__get__方法.

I think the better way is to mock the property as PropertyMock, rather than to mock the __get__ method directly.

在文档中进行了说明，搜索unittest.mock.PropertyMock: 拟用作类的属性或其他描述符的模拟. PropertyMock提供了__get__和__set__方法，因此您可以在获取返回值时指定其返回值.

It is stated in the documentation, search for unittest.mock.PropertyMock: A mock intended to be used as a property, or other descriptor, on a class. PropertyMock provides __get__ and __set__ methods so you can specify a return value when it is fetched.

方法如下:

class MyClass:
    @property
    def last_transaction(self):
        # an expensive and complicated DB query here
        pass

def test(unittest.TestCase):
    with mock.patch('MyClass.last_transaction', new_callable=PropertyMock) as mock_last_transaction:
        mock_last_transaction.return_value = Transaction()
        myclass = MyClass()
        print myclass.last_transaction
        mock_last_transaction.assert_called_once_with()

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