That just means you're putting a boundary when it's not necessary. Mox exists to make tests simpler to write and reason about, if you keep hitting extra layers of indirections then, "you're holding it wrong."
Most things are best used sparingly. That said, the vast majority of developers, even senior, have a very limited understanding of testing practices, and tend to create millions of separated, isolated modules, for no reason whatsoever. That's not Mox's fault.
A stupid example in practice: a naive blog app does not need Mox at all. If you add SSO sign up, you might want to put a boundary there to unit test without needing to set up a fake auth server, but 99% of your code won't ever touch it, just the authentication tests. Tomorrow you add payments, you might want to put a boundary just before your StripeRestAPI module to test the entire payment flow without contacting Stripe in your unit tests. Again, only the payment module tests ever need to touch Mox, the rest of your code doesn't. You place it before modules in the outer edge that have real-world side effects, not to isolate your functional and mostly pure core.
> And I just can’t justify it with “one day I might want to swap out the implementation”. YAGNI and if you do, deal with it then.
I agree with that. Using Mox to swap out implementations is a possible use case, but in practice it's better to hardcode things rather than trying to make it generic and swappable the first time around. Junior devs have a tendency to over-engineer code "because we might need to change it later." My motto is "copy and paste it three times before adding a layer of abstraction"
I hope you see the irony in using “you’re holding it wrong” here?
If real world use of a library tends to push towards a certain outcome that I dislike, I’m going to tend to dislike that library.
You’re also never going to convince me that creating an interface for a single implementation is the best way to facilitate unit testing.
Mox is nothing more than a kludge to get around the limitations of the language and I think there are much less invasive kludges available. To be honest when I’m working with devs who are new to elixir I’m embarrassed when I have to explain how Mox works.
>but in practice it's better to hardcode things rather than trying to make it generic and swappable the first time around. Junior devs have a tendency to over-engineer code "because we might need to change it later." My motto is "copy and paste it three times before adding a layer of abstraction"
> Mox is nothing more than a kludge to get around the limitations of the language and I think there are much less invasive kludges available. To be honest when I’m working with devs who are new to elixir I’m embarrassed when I have to explain how Mox works.
We spoke about this topic for far too long today, but looking at Mimic and its "nothing is mocked unless I tell you to" design, it works only iff you are using mocks the wrong way and at the wrong boundaries.
There’s no reason you can’t setup your tests so that mimic stubs out your module or a subset of functions in your module everywhere where you don’t explicitly override it.
The main difference is that the extra dispatch layer is only injected at test time, so there’s no extra indirection in the production code.
> I hope you see the irony in using “you’re holding it wrong” here?
Not really. If you use a hammer on a screw, is it the hammer's fault? Sounds like the code base you are working on is badly-organised, rather than Mox being the root of all evil. There are far too many stories of people picking up Elixir and coding in it as if it were Python or Ruby. You cannot base your experience with it on a codebase written by people new to functional languages.
And no one forces you to use Mox, anyway. It's far from being a core Elixir component. It is just one implementation of the mock object pattern that comes on a standalone, optional library.
> Mox is nothing more than a kludge to get around the limitations of the language
Mocks are not an Elixir invention, and exist in pretty much all languages.
> Mox is nothing more than a kludge to get around the limitations of the language and I think there are much less invasive kludges available.
You're definitely using or setting up mox wrong. Mox is incredibly good: it lets you do things in elixir that you definitely can't do in other languages: concurrently running tests with different mocks.
Such confidence, how do you approach testing your clients? Personally I have never used Mox, but I read the originating blog post when it came out and have followed it's principles ever since.
By either using Bypass, passing in fake adapters to Req, or injecting a dispatch layer at test time with Mimic.
I’ve been doing this for 20 years, you’re definitely never going to convince me that an interface for a single implementation is the best way to create the dynamic dispatch you need for testing.
Bypass is a nice alternative if the client is what's under test. Often it's not.
> passing in fake adapters to Req, or injecting a dispatch layer at test time with Mimic.
I see, so you buy into DI for the purposes of testing but you prefer a more terse approach than what behaviours offer. The extra module never really bothered me and the contents are mostly what would go into the implementation anyway. LSP provides documentation all the same.
> I’ve been doing this for 20 years, you’re definitely never going to convince me
I certainly appreciate your input, I like to learn new things, but have little interest in trying to convince anyone that makes such a dogmatic statement. An unfortunate thing to hear from a principle developer. I hope your coworkers agree with you.
Most things are best used sparingly. That said, the vast majority of developers, even senior, have a very limited understanding of testing practices, and tend to create millions of separated, isolated modules, for no reason whatsoever. That's not Mox's fault.
A stupid example in practice: a naive blog app does not need Mox at all. If you add SSO sign up, you might want to put a boundary there to unit test without needing to set up a fake auth server, but 99% of your code won't ever touch it, just the authentication tests. Tomorrow you add payments, you might want to put a boundary just before your StripeRestAPI module to test the entire payment flow without contacting Stripe in your unit tests. Again, only the payment module tests ever need to touch Mox, the rest of your code doesn't. You place it before modules in the outer edge that have real-world side effects, not to isolate your functional and mostly pure core.
I recommend the DestroyAllSoftware talks, especially https://www.destroyallsoftware.com/talks/boundaries
> And I just can’t justify it with “one day I might want to swap out the implementation”. YAGNI and if you do, deal with it then.
I agree with that. Using Mox to swap out implementations is a possible use case, but in practice it's better to hardcode things rather than trying to make it generic and swappable the first time around. Junior devs have a tendency to over-engineer code "because we might need to change it later." My motto is "copy and paste it three times before adding a layer of abstraction"