def test_subclass_of_a_dataclass_supported() -> None:
    """https://github.com/pydantic/pydantic/issues/3011"""

    @dataclasses.dataclass
    class A:
        thing_a: str

    class B(A):
        thing_b: str

    @pydantic.dataclasses.dataclass
    class C:
        thing: A

    b = B('Thing A')
    c = C(thing=b)
    assert c.thing.thing_a == 'Thing A'
https://github.com/pydantic/pydantic/issues/3011
tests/test_dataclasses.py