pytest magic

conftest.py

def pytest_collection_modifyitems(items, config):
    selected_items = []
    deselected_items = []

    for item in items:
        if 'new_fixture' in getattr(item, 'fixturenames', ()):
            selected_items.append(item)
        else:
            deselected_items.append(item)
    config.hook.pytest_deselected(items=deselected_items)
    items[:] = selected_items

test_foobar.py

import pytest


@pytest.fixture
def new_fixture():
    return 'foobar'


@pytest.fixture
def another_fixture(new_fixture):
    return 'foobar'


def test_abc(new_fixture):
    assert True


def test_def(another_fixture):
    assert False


def test_that_does_not_use_fixture():
    assert False