无法模拟从另一个 class（creates/uses 单例对象）继承的 class

Question

我有三个 classes 和一个单元测试用例： 1) A.py:

class A(object):
    def __new__(cls):
        """
         Overriding the __new__ method to make the A a singleTon class
         :return: cls.instance
         """
        if not hasattr(cls, 'instance') or not cls.instance:
             cls.instance = super(A, cls).__new__(cls)
             return cls.instance
        def execute():
             print("class A")
             return "Coming from class A"

2) B.py:

from A import A
class B(object):
    def __init__(self):
        """
         Initialize and declare any members/methods that can be passed over class that inherit this class
        """
        self.a = A()
        self.name = Name()
    def run(self):
        pass

class Name:
    def __init__(self):
        self.test_dict = {}

3) C.py

from B import B
class C(B):
    def __init__(self):
        super(C, self).__init__()
        self.result = None

    def run(self):
        self.result = self.A.execute()
        return self.result

4) test.py

import unittest
from unittest.mock import patch
from A import A
from B import B
from C import C

class TestMethods(unittest.TestCase):

    @patch('A.A')
    def test_basic(self, MockA):
        a = MockA()
        a.execute.return_value = "Testing code"

        c = C()
        result = c.run()
        self.assertEqual(result,"Testing code")

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

在执行 test.py 时，出现以下错误：

错误：test_basic（main.TestMethods）

Traceback (most recent call last):

File "C:\Users\davinder\AppData\Local\Continuum\Anaconda3\lib\unittest\mock.py", line 1179, in patched
   return func(*args, **keywargs)
File "C:/Users/davinder/PythonCodes/Test Framework/test.py", line 14, in test_basic
   c = C()
File "C:\Users\davinder\PythonCodes\Test Framework\C.py", line 5, in __init__
   super(C, self).__init__()
 File "C:\Users\davinder\PythonCodes\Test Framework\B.py", line 8, in __init__
    self.a = A()
 File "C:\Users\davinder\PythonCodes\Test Framework\A.py", line 8, in __new__
    cls.instance = super(A, cls).__new__(cls)
 TypeError: super() argument 1 must be type, not MagicMock

 ----------------------------------------------------------------------
 Ran 1 tests in 0.018s

 FAILED (errors=1)

我想通过使用 test.py 中使用的不同 return 值（通过修补）从 class C.py 中测试运行()。预先感谢您的帮助

编辑：即使我在 test.py 中模拟 C，像这样：

import unittest
from unittest.mock import patch
from A import A
from B import B
from C import C
from B import Name

class TestMethods(unittest.TestCase):

    @patch('C.C')
    @patch('A.A')
    def test_basic(self, MockA, MockC):
        a1 = MockA()
        a1.execute.return_value = "Testing code"

        c = MockC()
        c.a = a1
        c.name = Name()

        result = c.run()
        self.assertEqual(result,"Testing code")

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

出现此错误：

FAIL: test_basic (__main__.TestMethods)
----------------------------------------------------------------------
Traceback (most recent call last):
    File "C:\Users\davinder\AppData\Local\Continuum\Anaconda3\lib\unittest\mock.py", line 1179, in patched
        return func(*args, **keywargs)
    File "C:/Users/davinder/PythonCodes/Test Framework/test.py", line 22, in test_basic
        self.assertEqual(result,"Testing code")
 AssertionError: <MagicMock name='C().run()' id='2464384921272'> != 'Testing code'

 ----------------------------------------------------------------------
 Ran 1 tests in 0.018s

 FAILED (failures=1)

Answer 1

我不得不将 B.py 中的导入更改为 import 而不是 from。错误是因为 A 是从 B 模块中查找的，所以你的补丁必须是 @patch('B.A')。无论如何，这是关于该主题的有用读物：http://www.voidspace.org.uk/python/mock/patch.html#where-to-patch

现在，这是更改后的代码：

"""test.py"""
import unittest
from unittest.mock import patch
from c_module import C

class TestMethods(unittest.TestCase):
    @patch('b_module.A')
    def test_basic(self, mock_a):
        mock_a.return_value.execute.return_value = "Testing code"
        c = C()
        result = c.run()
        self.assertEqual(result,"Testing code")

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

"""c_module.py"""
from b_module import B
class C(B):
    def __init__(self):
        super(C, self).__init__()
        self.result = None
    def run(self):
        self.result = self.a.execute()
        return self.result

"""b_module.py"""
from a_module import A
class B(object):
    def __init__(self):
        """
         Initialize and declare any members/methods that can be passed over class that inherit this class
        """
        self.a = A()
        self.name = Name()
    def run(self):
        pass

class Name:
    def __init__(self):
        self.test_dict = {}

"""a_module.py"""
class A(object):
    def __new__(cls):
        """
         Overriding the __new__ method to make the A a singleTon class
         :return: cls.instance
         """
        if not hasattr(cls, 'instance') or not cls.instance:
             cls.instance = super(A, cls).__new__(cls)
             return cls.instance
        def execute():
             print("class A")
             return "Coming from class A"

我还鼓励您更改模块命名。在处理此问题时，很难不将模块与类混为一谈。你可以在上面看到我已经将模块名称更改为蛇形并保留类原样。

无法模拟从另一个 class（creates/uses 单例对象）继承的 class

Unable to Mock class that inherits from another class (which creates/uses singleton object)

python

unit-testing

patch

mocking

错误：test_basic（main.TestMethods）