test_things.py

import pytest


class Fixture():
    @property
    def foo(self):
        raise NotImplementedError


@pytest.fixture
def myfix():
    return Fixture()


@pytest.fixture
def child_fix1(myfix):
    myfix.foo = "bar"
    return myfix


@pytest.fixture
def child_fix2(myfix):
    myfix.foo = "baz"
    return myfix


def test_things(myfix, child_fix1, child_fix2):
    with pytest.raises(NotImplementedError):
        myfix.foo
    assert child_fix1.foo == "bar"
    assert child_fix2.foo == "baz"