[Haskell-cafe] Replacing IO with pure values

[David Thomas]

Depending on your scope, one thing you could do is replace the things
that operate against IO with functions that operate against some other
interface, and then provide an IO-based implementation and a pure
implementation of that interface.

That works best where the IO activity is fairly simple; of course,
when that's true you can often find ways to factor it out and just get
yourself a pure function to test anyway.  It works worst when you're
calling out into complicated libraries that live in IO.  There may be
a sweet spot between these two where it would be a good fit.

On Mon, Nov 24, 2014 at 8:26 AM, Corentin Dupont
<corentin.dupont at gmail.com> wrote:
> This Stackoverflow give a lot of hints:
> http://stackoverflow.com/questions/7370073/testing-functions-in-haskell-that-do-io
>
> You cannot "Unit" test functions that performs IO, because by definition a
> unit test is about testing an isolated piece of code that give the same
> result for the same input, i.e. pure.
> In my programs I separate the non-IO parts for the IO parts, so that I can
> test the non-IO parts.
> The IO parts are mainly the GUI parts of my apps, which I test manually.
>
> Now it should be possible to trick the IO monad by supplying always the same
> user input to your function, but I don't know how to do that.t performs,
> because by definition a unit test is about testing an isolated piece of code
> that give the same result for the same input, i.e. pure.
>
>
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