pytest_indirect_param_fixtures.py

# https://docs.pytest.org/en/latest/example/parametrize.html#apply-indirect-on-particular-arguments

import pytest


class SomeClass:
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

    def add_all(self):
        return self.a + self.b + self.c


@pytest.fixture(scope='module')
def some_class(request):
    return SomeClass(**request.param)


class TestSomeClass:
    @pytest.mark.parametrize('some_class,expected', [
        ({"a": 2, "c": 3, "b": 5}, 10)
    ], indirect=["some_class"])  # indirect tells this method which args are fixtures to parameterize
    def test_add_all(self, some_class, expected):
        assert some_class.add_all() == expected
        
# if we want to also monkeypatch attributes/methods of some_class, we can change the some_class fixture to:
# Learn more about how to use the monkeypatch fixture:
# https://stackoverflow.com/a/37201584. # no import required
# https://docs.pytest.org/en/stable/monkeypatch.html  # examples
@pytest.fixture(scope='module')
def some_class(request, monkeypatch):
    instance = SomeClass(**request.param)
    monkeypatch.setattr(instance, "c", 100)  # attrs must already exist to be monkeypatched
    yield instance  # note this has to be yield, not return