Efx - A library to declaratively write testable effects

Does this mean there is a minimum version of OTP required?

To ask a fairly obviously question, the idea is that any side-effect functions (or just ones you want to test) can be defined with defeffect? So MyModule in the README example is the implementation/domain code? If so that’s super cool.

I am not sure I get the idea at all… are effects completely opt-in and whatever the dev says are effects? I’d expect a library like this to scan my code for e.g. File.write and automatically tag the function calling it as effectful.

But I am likely severely misunderstanding here.

I’m glad I’m not the only one who was slightly confused! I think the README could be slightly more explicit in the examples.

But yes, I’ve just been playing with it in a demo app and you simply define your application’s functions with defeffect then you can mock them in tests with bind. It’s not auto-flagging side-effects for you. It feels pretty nice. I kind of want to use defeffect for all side-effect functions even if I don’t mock them in tests (though I probably won’t).

Yeah, there’s a small example in tests/support.

I think it would be clearer if the examples actually had effectul code in the bodies just to drive the point home, especially for those of us who skim code examples on first read-through of READMEs. But like, I figured it out

There are also a couple of small gotchas not explicitly documented: @specs aren’t optional (which makes sense) and zero-arity functions are required to be defined with empty () or else you get a cryptic error. I opened an issue about the latter.

So it’s more or less a mocking library?

Yes indeed

It is a mocking library, that doesn‘t need global binding for your test cases. So all mocking and preparation happens directly in your test code. No need for configs or anything else.

I started using it in my projects and it makes testing clearer and easier.

Kudos to @murrgelb