mock.patch 在 with 语句的范围之外泄漏模拟对象

Question

我在文件夹controller/下有以下三个python文件

1. 数学.py

class Math:
    def __init__(self, a, b):
        self.a = a
        self.b = b

    def addition(self):
        return self.a + self.b

2. 计算.py

from controller.math import Math


def perform_addition():
    math = Math(1, 2)
    return math.addition()

3. 测试样本.py

from unittest.mock import MagicMock, patch

def test_addition():


    mock_math = MagicMock()

    with patch('controller.math.Math', return_value=mock_math) as MockClass:
        instance = MockClass.return_value

        instance.addition.return_value = 100

        from controller.calculation import perform_addition
        output = perform_addition()

        print(output)  # prints 100

    post_patch_output = perform_addition()
    print(post_patch_output)  # prints 100 but expected 3

当我执行 test_addition 时，我期望

post_patch_output

返回 3，但它返回 100，即模拟输出。我很好奇我在这里错过了什么？

从mock.patch的文档这里，它说

When the function/with statement exits the patch is undone.

这看起来不像这里的情况

Answer 1

功能修正

test_addition

您必须修改文件

test_sample.py

，如下所示：

from unittest.mock import MagicMock, patch
from controller.calculation import perform_addition

def test_addition():

    mock_math = MagicMock()

    #with patch('controller.math.Math', return_value=mock_math) as MockClass:
    with patch('controller.calculation.Math', return_value=mock_math) as MockClass:
        instance = MockClass.return_value

        instance.addition.return_value = 100

        #from controller.calculation import perform_addition
        output = perform_addition()
        print(output)  # prints 100

    post_patch_output = perform_addition()
    print(post_patch_output)  # prints 100 but expected 3

test_addition()

这是执行

test_addition()

的输出：

100
3

如你所料。

代码中的错误

• 您必须在文件

  Math

  内而不是在

  calculation.py

   内修补由名称 

  math.py
引用的对象
• 之前的修改就足够了，但我更喜欢在文件顶部执行导入

  from controller.calculation import perform_addition

  ，而不是在方法内部

  test_addition