Background

Some time ago I manifested my dislike for using ETS tables because I saw them as Singletons, which bring a myriad of problems when testing. However @peerreynders linked me to the Just Create One pattern, spearheaded by our dear Uncle Bob.

Theoretical differences

I get the main difference. You can ask an app to create a Singleton a million times, and it will always return the same instance. With JCO, you can’t ask the app to create something a million times - you create it once and that’s it.

Practical differences

But in practice, specially when it comes to testing (which is what I am interested in), they are really both the same. You need a mock (mock as a noun) for each one, and once you bring either of them into your app, you basically forfeit concurrent tests because now you have a global state to worry about - which I dislike very much.

How do you test (or perhaps avoid?) something like a Singleton or a JCO instance and still allow for concurrent tests?

My only idea is to do functional injection, but then I have to pass a (huge) list of dependencies to every function. It is rather discouraging from a design perspective, as you literally need to pass around the whole jungle so you can tell a Gorilla to eat his freaking banana.

Discussion time

Any ideas on how to fix this, testing wise?