Usage with pytest

modern-di-pytest turns any DI dependency into a pytest fixture. Two callables cover the entire surface — modern_di_fixture for a single dependency and expose for bulk-generating one fixture per provider across one or more Group subclasses.

How to use

1. Install modern-di-pytest:

uvpippoetry

uv add --dev modern-di-pytest

pip install modern-di-pytest

poetry add --group dev modern-di-pytest

1. Define a di_container fixture at the highest pytest scope you want. The plugin never builds the container — you own it:

import typing

import modern_di
import pytest

from app import ioc


@pytest.fixture(scope="session")
def di_container() -> typing.Iterator[modern_di.Container]:
    with modern_di.Container(groups=ioc.ALL_GROUPS) as container:
        yield container

1. Materialize dependencies as fixtures, either in bulk via expose or one-by-one via modern_di_fixture:

from modern_di_pytest import expose, modern_di_fixture

from app.ioc import Auth, Billing, Dependencies
from app.services import EmailClient


# Bulk: every Provider on each group becomes a pytest fixture
# named after the class attribute. Pass several groups in one call;
# duplicate names across groups raise ValueError. Non-Provider attributes
# are skipped.
expose(Dependencies, Auth, Billing)

# Manual: a single type or Provider as a named fixture.
email_client = modern_di_fixture(EmailClient)

1. Tests receive resolved dependencies by name:

from app.services import EmailClient, UserService


def test_listing(user_service: UserService) -> None:
    assert user_service.list_users() == []


def test_email(email_client: EmailClient) -> None:
    email_client.send("hi")

Pointing a fixture at a child container

Define the child-container fixture yourself, then pass its name via container_fixture=:

import typing

import modern_di
import pytest
from modern_di_pytest import modern_di_fixture

from app.services import UserService


@pytest.fixture
def request_container(
    di_container: modern_di.Container,
) -> typing.Iterator[modern_di.Container]:
    with di_container.build_child_container(scope=modern_di.Scope.REQUEST) as container:
        yield container


request_user_service = modern_di_fixture(
    UserService, container_fixture="request_container"
)

The same container_fixture= parameter is also accepted by expose, so one or more Group subclasses can be exposed against the request container.

Overrides

modern-di-pytest deliberately does not ship override sugar. Use Container.override() directly — it is already backed by a tree-shared OverridesRegistry:

import modern_di

from app.ioc import Dependencies
from app.services import UserService
from tests.fakes import FakeRepo


def test_with_override(
    di_container: modern_di.Container,
    user_service: UserService,
) -> None:
    di_container.override(Dependencies.user_repo, FakeRepo())
    try:
        assert user_service.list_users() == []
    finally:
        di_container.reset_override(Dependencies.user_repo)

When di_container is session-scoped, prefer to wrap the override in a function-scoped fixture so cleanup is guaranteed:

import typing

import modern_di
import pytest

from app.ioc import Dependencies
from tests.fakes import FakeRepo


@pytest.fixture
def mock_user_repo(di_container: modern_di.Container) -> typing.Iterator[None]:
    di_container.override(Dependencies.user_repo, FakeRepo())
    yield
    di_container.reset_override(Dependencies.user_repo)