python - 模拟父类 __init__ 方法

Question

我正在尝试在派生自另一个类的类上编写一些单元测试，但我在模拟父类 init 方法时遇到一些困难，而 afaik 你做不到，所以我正在寻找建议.

这是我的类(class)的例子

导入.py

class Imported():
    def __init__(self, a="I am Imported"):
        print("a:{}".format(a))

父类.py

from Imported import Imported

class Parent(object):

    parent_list = ["PARENT"]

    def __init__(self, a="I am Parent"):
        imported = Imported(a)

派生.py

from Parent import Parent

class Derived(Parent):

    Parent.parent_list.append("DERIVED")

在我的单元测试中，当我从派生类 Derived() 实例化一个对象时，我想验证 Parent.parent_list == ["PARENT", "DERIVED"]。

这两种解决方案都行不通

test_Derived.py

import unittest
from mock import patch

from Derived import Derived


class test_Derived(unittest.TestCase):

    @patch("Derived.Parent.__init__")
    def test_init_001(self, mock_parent_init):
        a = Derived("I am Derived")
        mock_parent_init.assert_called_with("I am Derived")
        self.assertEquals(a.parent_list, ["PARENT", "DERIVED"])

    @patch("Derived.Imported.Imported")
    def test_init_002(self, mock_parent_init):
        a = Derived("I am Derived")
        mock_parent_init.assert_called_with("I am Derived")
        self.assertEquals(a.parent_list, ["PARENT", "DERIVED"])

test_init_001 失败

TypeError: __init__() should return None, not 'MagicMock'

test_init_002 失败

ImportError: No module named Parent.Imported

有什么建议吗？

Answer 1

对于第一种方案，将__init__方法的返回值改为None。

@patch("Derived.Parent.__init__")
def test_init_001(self, mock_parent_init):
    mock_parent_init.return_value = None  # <---
    a = Derived("I am Derived")
    mock_parent_init.assert_called_with("I am Derived")
    self.assertEquals(a.parent_list, ["PARENT", "DERIVED"])

对于第二种解决方案，修补Parent.Imported:

@patch("Parent.Imported")  # <---
def test_init_002(self, mock_parent_init):
    a = Derived("I am Derived")
    mock_parent_init.assert_called_with("I am Derived")
    self.assertEquals(a.parent_list, ["PARENT", "DERIVED"])