mock.patch applied at class level behaves incorrectly

Bug report

When applying @mock.patch to classes where the test_ method is inherited, this applies the patch to the base class,, instead of to the specific class. In this case, the patch to the g method applies in MockedFTests and MockedFStraightGTests.

# a.py
import unittest
from unittest import mock

def f():
    return 41

def g():
    return 43

class BaseFTests(unittest.TestCase):
    def test_a(self):
        self._asserts(f())

    def _asserts(self, val):
        print(self, val)

@mock.patch('a.f', new=lambda: 2)
class MockedFTests(BaseFTests):
    def _asserts(self, val):
        print(self, val)
        self.assertEqual(val, 2)
        self.assertEqual(g(), 43)

@mock.patch('a.g', new=lambda: 3)
class MockedFMockedGTests(MockedFTests):
    def _asserts(self, val):
        print(self, val)
        self.assertEqual(val, g()-1)

class MockedFStraightGTests(MockedFTests):
    def _asserts(self, val):
        print(self, val)
        self.assertEqual(val, 2)
        self.assertEqual(g(), 43)

Expect all tests to pass.
Actual output: 2 tests fail with error AssertionError: 3 != 43

Your environment

• CPython versions tested on: Python 3.10.4 on Windows

Start by reproducing the example in a small module using unittest.mock.patch, focusing on inherited test_ methods and the classes BaseFTests, MockedFTests, MockedFMockedGTests, and MockedFStraightGTests. Trace the class-level patch behavior in unittest.mock and add a regression test for the reported inheritance case. Done means the example's tests pass without applying the subclass patch to sibling classes.