from unittest.mock import Mock
from dataclasses import fields, dataclass


def create_dataclass_mock(obj):
    return Mock(spec=[field.name for field in fields(obj)])


@dataclass
class A:
    aaa: str
    bbb: int


simpleMock = Mock()
specialMock = create_dataclass_mock(A)

simpleMock.aaa  # returns a mock (Good)
specialMock.aaa # returns a mock (Good)

simpleMock.attribute_that_should_not_exist  # returns a mock (Bad)
specialMock.attribute_that_should_not_exist # raises an exception (Good)