Testing

Quickstart

You can create a fixture in conftest.py that provides a ServiceProvider instance:

@pytest.fixture
async def service_provider() -> AsyncGenerator[ServiceProvider]:
    async with services.build_service_provider() as service_provider:
        yield service_provider

And then you can inject it into your tests and resolve the services.

async def test_create_user(service_provider: ServiceProvider) -> None:
    user_service = await service_provider.get_required_service(UserService)

    await user_service.create_user()

Globally override a service

Imagine you have a service EmailService that sends real emails. During testing, you want to replace it with a mock implementation that doesn't send real emails.

@pytest.fixture
async def service_provider(mocker: MockerFixture) -> AsyncGenerator[ServiceProvider]:
    email_service_mock = mocker.create_autospec(EmailService, instance=True)
    services.add_singleton(EmailService, email_service_mock)

    async with services.build_service_provider() as service_provider:
        yield service_provider

Remember that if EmailService is already registered in services, adding it again will override the previous registration. Now, when you resolve EmailService in your tests, you'll get the mock implementation instead of the real one.

Override a service per test

You can also override a service for a specific test case. This is useful when you want to test different behaviors of a service.

async def test_create_user(
    service_provider: ServiceProvider,
    mocker: MockerFixture
) -> None:
    email_service_mock = mocker.create_autospec(EmailService, instance=True)
    services.add_singleton(EmailService, email_service_mock)
    user_service = await service_provider.get_required_service(UserService)

    await user_service.create_user()

But given services is a singleton declared in main.py, you should instead create in main.py the function configure_services that returns a new ServiceCollection each time you call it, so that each test can call it to get a fresh ServiceCollection instance.

def configure_services() -> ServiceCollection:
    services = ServiceCollection()
    services.add_transient(EmailService)
    return services

Regarding the fixture setup, it'd look like this:

@pytest.fixture
def services() -> ServiceCollection:
    return configure_services()

@pytest.fixture
async def service_provider(services: ServiceCollection, mocker: MockerFixture) -> AsyncGenerator[ServiceProvider]:
    email_service_mock = mocker.create_autospec(EmailService, instance=True)
    services.add_singleton(EmailService, email_service_mock)

    async with services.build_service_provider() as service_provider:
        yield service_provider

And the test case:

async def test_create_user(services: ServiceCollection, mocker: MockerFixture) -> None:
    email_service_mock = mocker.create_autospec(EmailService, instance=True)
    services.add_singleton(EmailService, email_service_mock)

    async with services.build_service_provider() as service_provider:
        user_service = await service_provider.get_required_service(UserService)

        await user_service.create_user()