DI - Adding basic manual injection

[hamorillo]

#14

I did some research about DI in libraries. What I've seen is that, in general, libraries don't usually use another library for the DI. I would say there are two main reasons for that:

• Avoid adding another external dependency in the library that you'll need to release within your artifact.
• Prevent the library clients from dependency conflicts.

My first idea was to search for libraries using HILT. The short answer is: You can't use HILT in a library (If you don't fully control the app that is going to use the library at it also uses HILT, so it's not a valid solution for a public library).

Dagger is definitely a viable option. There is a limited amount of info on the internet, and I couldn't find several projects using it.

I didn't investigate Koin, but I'm pretty sure we could use it if we wanted.

Taking the previous info into account plus the expected side/complexity of our library, I think the best option for us is to use basic manual injection. Basically, to be able to implement good quality tests without. You can find a basic example here.

This PR follows the Google example and creates a test to verify the idea behind the manual injection.

Please, feel free to leave your comments. I'm opening the discussion about DI with this PR.

[hamorillo]

Using Mockk for mocking objects. It's more modern and designed for Kotlin code.

More info:

Mockito vs Mockk
Mockk GuideBook

[maxme]

TIL about Mockk, thanks for the links

[mlumeau]

Good first implementation but as we quickly grow the codebase we'll need to split GravatarSDKContainer into sub-containers (network, image loading, oauth flow, db, ...)

[maxme]

LGTM

I didn't investigate Koin, but I'm pretty sure we could use it if we wanted.

Honestly I'd like to remove some boiler code (maybe by testing/using Koin), but I'd also like to avoid an extra dependency. So I'm fine using manual injection first, we can revisit this later if it becomes a pain to manage. Good thing, it won't impact the end users (developers) if we swap it with Koin.