mock.seal changes behavior of isinstance for generic classes

[torfsen]

Bug report

Bug description:

from unittest.mock import Mock, seal

class Foo:
    pass

class Bar[T]:
    pass

for cls in [Foo, Bar]:
    print(cls.__name__, "unsealed:", isinstance(Mock(cls), cls))

    m = Mock(cls)
    seal(m)
    print(cls.__name__, "sealed:", isinstance(m, Foo))

With both Python 3.12.7 and 3.13.7 this prints

Foo unsealed: True
Foo sealed: True
Bar unsealed: True
Bar sealed: False

I would have expected that sealing a mock does not change its behavior w.r.t. isinstance.

CPython versions tested on:

3.13

Operating systems tested on:

Linux

[torfsen]

Nevermind, typo in the example.

[torfsen]

FWIW, my original issue turned out to be related to Pydantic: pydantic/pydantic#12259.