Export TestDouble Function in Hex Package

[nelsonic]

At present we are not explicitly exporting the Mock version of HTTPoison in our Hex package.
Which means that the we need to have a Mock implementation in each "consumer" project.
See: https://github.com/dwyl/auth-mvp/blob/9836d31b501a731fcedfdd8a0d4fe026d105bda2/lib/mock/elixir_auth_google.ex#L1-L27

I propose that we take this a step further and actually check the MIX_ENV in the elixir-auth-google package and if MIX_ENV=test we return the Mock version of the functions.
e.g: https://github.com/dwyl/elixir-auth-google/blob/master/lib/httpoison/in_memory.ex
This way the person using the package never has to think about creating their own mocks and simply copy-paste the sample tests to achieve 100% test coverage in their project.

I don't know if this is an "anti pattern" or a "best practice" so I've opened a question to find out:
https://softwareengineering.stackexchange.com/questions/408267/is-it-a-best-practice-or-anti-pattern-to-export-mock-versions-of-functions-for-a

Asking questions is the only way to learn. If you aren't asking questions you aren't learning.

I think I want to export the Mocks regardless of what other people say - because I don't want to have to duplicate this code in the Auth project - but I'm curious what the "best practice" is.

[SimonLab]

I propose that we take this a step further and actually check the MIX_ENV in the elixir-auth-google package and if MIX_ENV=test we return the Mock version of the functions.
e.g: https://github.com/dwyl/elixir-auth-google/blob/master/lib/httpoison/in_memory.ex
This way the person using the package never has to think about creating their own mocks and simply copy-paste the sample tests to achieve 100% test coverage in their project.

I like this idea. Having an test example as documentation for the users should be enough for them to cover the authentication testing. At the moment I don't see any cases where the users would want to customise the return values of the mock but it could be added later on if necessary.

[nelsonic]

Got a reply on StackExchange:

The correct technical term is a "TestDouble".
I'm going to make an attempt at this and will assign the PR when ready. 👍

[nelsonic]

Sadly, Module attribute based dependency injection did not work.
So I had to go searching ...
https://blog.carbonfive.com/2018/03/19/lightweight-dependency-injection-in-elixir-without-the-tears
Using a function to inject the dependency worked. 👍

[nelsonic]

PR: #36

[nelsonic]

It never ceases to amaze me how some people down-vote questions ...

Some people just don't have anything better to do so they have crap on others. 🤦‍♂

[nelsonic]

Meanwhile, there are a couple of answers on my original SoftwareEngineering question.
Exporting a TestDouble is very much a standard practice
and we have applied it to several of our projects now. 👍