DocTest VS registry

doctest for testing examples in the documentation. Docs are much clearer when they contain usage examples and doctest helps them keep up to date.

Try to restrict your types even on sub functions (inside where), use testing, break down your code to the most atomic parts, using ghci to debug each part once at a time, and because Haskell doesn't let you reuse variables, or mutate state, it's a lot easier to rationalize evaluation order (which makes it a lot easier to debug without step debuggers compared to languages like python).

Some may argue that the tests are a form of documentation, and that's true, but they still don't capture the why. And tests are almost always separated from the actual code, which makes it more complicated to look at the code and the tests at the same time and understand them together. I've used doctest with Haskell which is a solution to this. Doctest is nice at first but in my experience it wasn't reasonable to do non-trivial tests in doctest, and plenty of tests are non-trivial. So then you're left with the decision to use doctest where you can, and another test solution for non-trivial tests, or just do all tests using the other testing solution. We chose simplicity and got rid of doctest.

Additionally I have some code to run one Test (single test or test group) from GHCi by passing the function name (run) or a subset of the tests by passing a regexp of the description (runOnly). You can find some of those functions here: https://github.com/etorreborre/registry/blob/main/test/Test/Tasty/Extensions.hs.

u/henry_kwinto I just want to mention that if you end-up having quite a few of those `makeXXX` functions you can put them in a registry and the wiring will be done automatically for you.

Then, the registry library provides point 2 by allowing to "stack" all the constructor functions for your components and override them at will: