修补模拟类的方法 [英] Patch a method of a mocked class

问题描述

我的代码结构如下:

我有一个从 BaseClass 继承的 MyClass 类(这是一个偶然的点，而不是我的问题的根源).然后我有另一个类 MyClassManager 调用 MyClass 的方法.

I have a class MyClass that inherits from BaseClass (this is an incidental point and not the source of my problem). Then I have another class MyClassManager that calls the methods of MyClass.

我正在为 MyClassManager 的方法编写单元测试，我想控制 MyClass 方法之一的返回值，同时自动指定其余方法.

I am writing a unittest for a method of MyClassManager and I want to control the return value of one of the methods of MyClass while autospeccing the rest.

在我的测试中，我通过使用 autospec=True 修补类，为 MyClass 创建了一个 Mock.然后我尝试修补方法 MyClass.method_to_patch 并将其替换为 Substitute.substitute_method.到目前为止，一切都很好.

In my test I have created a Mock for MyClass by patching the class with autospec=True. Then I have tried to patch the method MyClass.method_to_patch and replace it with Substitute.substitute_method. So far, so good.

但是现在当我运行测试时，类管理器创建了一个 MyClass 的实例，它是一个完全自动指定的 Mock，但它没有修补我想要替换的方法.

But now when I run the test, the class manager creates an instance of MyClass that is a fully autospecced Mock, but it doesn't patch the method I want to substitute.

有没有办法结合这两个 patch 装饰器来实现我想要的?

Is there a way to combine these two patch decorators to achieve what I want?

class Substitute:

    def substitute_method(self, arg1, arg2):
        print("Running substitute method")
        return (arg1 > 0 and arg2 > 0)


class BaseClass:

    def method_to_patch(self, arg1, arg2):
        return arg1 == arg2


class MyClass(BaseClass):

    def myclass_method(self):
        print("myclass method called")


class MyClassManager:

    def method_to_test(self):
        my_class = MyClass()
        my_class.myclass_method()
        my_class.method_to_patch(10, 100)


class TestMyClass(unittest.TestCase):

    @patch.object(MyClass, "method_to_patch", Substitute.substitute_method)
    @patch("__main__.MyClass", autospec=True)
    def test_method_to_test(self, mock_class):
        class_manager = MyClassManager()
        class_manager.method_to_test()
        print(mock_class.call_count)


if __name__ == "__main__":
    unittest.main()

推荐答案

我在下一页找到了答案的线索，其中讨论了模拟嵌套属性调用:https://www.integralist.co.uk/posts/mocking-in-python/.相同的逻辑适用于方法调用.

I found a clue to the answer at the following page where it talks about mocking nested attribute calls: https://www.integralist.co.uk/posts/mocking-in-python/. The same logic applies to method calls.

手动调整模拟对象是不够的 - 你必须调整模拟对象的return_value.

It is not enough to manually adjust the mocked object - you have to adjust the return_value of the mocked object.

这里是测试的样子:

class TestMyClass(unittest.TestCase):

    @patch("__main__.MyClass", autospec=True)
    def test_method_to_test(self, mock_class):
        mock_class.return_value.method_to_patch = Substitute.substitute_method
        class_manager = MyClassManager()
        class_manager.method_to_test()
        print(mock_class.call_count)

现在我有一个模拟对象代替了 MyClass 所以 MyClass.myclass_method 也被模拟了，但我可以替换 Substitute.substitute_methodMyClass.method_to_patch 我想要的地方.

Now I have a mock object in place of MyClass so MyClass.myclass_method is also mocked, but I can substitute Substitute.substitute_method in place of MyClass.method_to_patch as I wanted.

最后一点 - substitute_method 实际上是一个 staticmethod 所以它应该是这样的:

One final note - the substitute_method is actually a staticmethod so it should look like this:

class Substitute:

    @staticmethod
    def substitute_method(arg1, arg2):
        print("Running substitute method")
        return (arg1 > 0 and arg2 > 0)

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