Python单元测试模拟类和类方法

我觉得这可能相对简单，但我正在费尽心思才能让它发挥作用。我想模拟整个类，然后指定该类的方法之一的返回值。

我已经看过了here，在其他几个问题上，当然还有docs。我仍然无法让它发挥作用。请参阅下面我的简单示例。

目录内容tmp:

tmp
├── __init__.py
├── my_module.py
└── test_my_module.py

内容my_module.py:

class MyClass:
    def __init__(self):
        # Do expensive operations that will be mocked in testing.
        self.a = 7

    def my_method(self):
        # For sake of simple example, always return 1.
        return 1


def create_class_call_method():
    """Create MyClass instance and call its my_method method, returning
    the result."""
    instance = MyClass()
    value = instance.my_method()
    return value

内容test_my_module.py:

import unittest
from unittest.mock import patch, Mock

from tmp import my_module


class MyClassTestCase(unittest.TestCase):

    def test_create_class_call_method(self):
        # Attempt to patch MyClass as well as specify a return_value for
        # the my_method method (spoiler: this doesn't work)
        with patch('tmp.my_module.MyClass',
                   my_method=Mock(return_value=2)):
            value = my_module.create_class_call_method()

        self.assertEqual(value, 2)


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

运行结果test_my_module.py:

2 != <MagicMock name='MyClass().my_method()' id='140234477124048'>

Expected :<MagicMock name='MyClass().my_method()' id='140234477124048'>
Actual   :2

我尝试过的其他一些事情：

• 而不是..., my_method=Mock(return_value=2)) in the patch语句，像这样解压字典：**{'my_method.return_value': 2}
• Nested with patch声明。外部语句很简单，例如with patch('tmp.my_module.MyClass'):，内部语句尝试修补my_method像这样：with patch('tmp.my_module.MyClass.my_method, return_value=2)
• 使用补丁装饰器而不是上下文管理器
• 将补丁声明更改为with patch('tmp.my_module.MyClass') as p:然后在里面with语句，尝试设置p像这样：p.evaluate = Mock(return_value=2)

如有任何帮助，我们将不胜感激，谢谢。

我找到了一个更好的解决方案。简而言之，我们需要模拟return_value of the MyClass嘲笑。这是工作测试代码：

import unittest
from unittest.mock import patch, Mock, MagicMock

from tmp import my_module


class MyClassTestCase(unittest.TestCase):

    def test_create_class_call_method(self):
        # Create a mock to return for MyClass.
        m = MagicMock()
        # Patch my_method's return value.
        m.my_method = Mock(return_value=2)

        # Patch MyClass. Here, we could use autospec=True for more
        # complex classes.
        with patch('tmp.my_module.MyClass', return_value=m) as p:
            value = my_module.create_class_call_method()

        # Method should be called once.
        p.assert_called_once()
        # In the original my_method, we would get a return value of 1.
        # However, if we successfully patched it, we'll get a return
        # value of 2.
        self.assertEqual(value, 2)


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

以及成功的结果：

Ran 1 test in 0.002s

OK