How do I override the FastAPI dependencies in a test?

[Hughes1978]

I understand how to manually override and inject parameters into a method, but how do I override them for a test run?

When testing FastAPI endpoints, I can override the dependencies with dependency_overrides.
Those don't work when using fastapi-injectable, and overriding them for a particular function only works if I do not have any calls in between.

Right now, I have this:

class _Poller(Worker):
    @override
    def process_work(self, job: Job) -> None:
        self._process_work_implementation(job) # type: ignore -> dependency injection solves this

    @injectable
    def _process_work_implementation(self, job: Job, publishing_service: dependencies.PublishingService) -> None:
        ...

In the above, in a test, I can call like this:

def some_test():
    mock_publishing_service = MagicMock(spec=PublishingService)
    mock_publishing_service.set_results.return_value = expected_results

    poller = _Poller()
    poller._process_work_implementation(job, publishing_service=mock_publishing_service)

But what I want is for this to work:

def some_test():
    mock_publishing_service = MagicMock(spec=PublishingService)
    mock_publishing_service.set_results.return_value = expected_results

    PROVIDE_OVERRIDE[dependencies.PublishingService] = lambda: mock_publishing_service

    poller = _Poller()
    poller.process_work(job)

Is there some kind of override context that I can hook into when using @Injectable ?

[JasperSui]

Hi,

You can refer to this example.

So you will still need to prepare a FastAPI app object even if it's not testing a FastAPI endpoint, then call register_app(app), finally use app.dependency_overrides[dependencies.PublishingService] = lambda: mock_publishing_service to override the dependency getter function.

[Hughes1978]

Thanks for the response!

Does register_app have to be called always, in every situation? Or only in tests / when not running from a FastAPI endpoint method?

[JasperSui]

If we're talking about the overriding the dependency, then yes, it's the only way for fastapi-injectable to keep using your FastAPI app object to pass when resolving the dependencies, and that's how app.dependency_overrides with @injectable works in this case.

If you don't care anything about those things that need FastAPI app object to be done, you can just use the @injectable and get_async_obj() without registering it.