Support FastAPI dependency overrides

Hi Steve,

Love the framework so far. One issue I’m having is in trying to use FastAPI dependency overrides in a similar manner to vanilla FastAPI, when making web-layer unit tests. I.e. mocking out dependencies.

In vanilla FastAPI you would do something like this (with pytest):

...
from fastapi.testclient import TestClient
from dependencies import get_foo_service  # <-- Dependency function
from foo import FooService
...

@pytest.fixture
def foo_service_mock():
    return Mock(FooService)

@pytest.fixture
def client(foo_service_mock) -> Generator:
    app.dependency_overrides[get_foo_service] = lambda: foo_service_mock

    with TestClient(app) as c:
        yield c

But I can’t see how I could replicate the override (app.dependency_overrides[get_foo_service]) functionality when using the Lagom FastAPI DI approach (i.e. when using deps.depends(FooService)).

I suppose I would somehow need to reference the inner _resolver function of depends…surely this isn’t possible?

Thus it would be nice if there were explicit support for FastAPI dependency overrides.

Thanks!

[meadsteve]

The work in #177 is now released as version 1.6.0. Let me know how you get on @rowanbarrie . I’ll close this issue but we can re-open it if there’s some use-cases I’ve not covered.

[meadsteve]

I went for a slightly different approach in #177 and returned a mutable container from the context manager rather than providing an update function/lambda. It felt easier to use and read.