Mocked value at method level not overriding class-level mock in unittest

Bug report

Bug description:

Description

I encountered an issue where mocking a value at the method level does not override the class-level mock in unit tests. Even though the method-level mock should take precedence, the value from the class-level mock is still being used.

Steps to Reproduce

Create a test class with a class-level mock using @mock.patch.
Add a method-level mock to one of the test methods to override the class-level mock.
Run the tests and observe that the class-level mock value is still used instead of the method-level mock.

Expected Behavior

The method-level mock should override the class-level mock, and the value set in the method-level mock should be used in the test.

Actual Behavior

The class-level mock value is used, and the method-level mock is ignored.

Sample code

import unittest
from unittest import mock

# Function to be mocked
def get_value():
    return "original"

# Class-level mock
@mock.patch('module.get_value', return_value='class-level')
class TestMock(unittest.TestCase):

    def test_class_level_mock(self, mock_get_value):
        # This should return 'class-level'
        result = get_value()
        self.assertEqual(result, 'class-level')

    @mock.patch('module.get_value', return_value='method-level')
    def test_method_level_mock(self, mock_get_value):
        # This should return 'method-level', but it returns 'class-level'
        result = get_value()
        self.assertEqual(result, 'method-level')

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

CPython versions tested on:

3.10

Operating systems tested on:

No response

首先，使用在类级别和方法级别都应用 unittest.mock.patch 的方式重现该示例，然后检查 unittest.mock.patch 装饰器及其与 unittest.TestCase 方法的交互。确认方法级别的返回值是否会被忽略，并添加或更新一个有针对性的回归测试，以展示预期的方法级别覆盖。