Use savePost in golden tests

[Minoru]

I wrote golden tests for Hakyll.Convert.Blogger.readPosts and Wordpress.readPosts. They rely on a Show instance for types that represent a post. The default implementation prints everything out in a single line, so when a test fails, it's quite hard to see what exactly the difference is.

Furthermore, Wordpress posts are represented by a type defined in an external library. Depending on its Show instance for testing is probably a bad idea.

These tests should be rewritten with savePost, which is our function. That will lean them towards integration testing, which is fine. We can then use tasty-mgolden to provide us with nice diffs on test failures.

Blocked on #19.

[Minoru]

tasty-mgolden is absent from LTS-6.9 that we currently use. If we add it as an extra-package, we run into problems with dependencies:

In the dependencies for tasty-mgolden-0.0.2:
    Diff-0.3.2 from stack configuration does not match ==0.3.4 || ==0.4.*  (latest matching version is 0.4.0)
    ansi-terminal-0.6.2.3 from stack configuration does not match >=0.9 && <0.11  (latest matching version is 0.10.3)
    base-4.8.2.0 from stack configuration does not match >=4.12 && <=4.15  (latest matching version is 4.14.0.0)
    filepath-1.4.0.0 from stack configuration does not match >=1.4.2 && <1.5  (latest matching version is 1.4.2.1)
    tasty-0.11.0.3 from stack configuration does not match >=1.3.1 && <1.4  (latest matching version is 1.3.1)
needed due to hakyll-convert-0.2.0.0 -> tasty-mgolden-0.0.2

Let's postpone migrating to tasty-mgolden, then.

[Minoru]

Actually, this is impossible to implement, since Blogger.readPosts and Wordpress.readPosts don't return DistilledPost that IO.savePost expects. We could get a DistilledPost by testing mapM Blogger.distill $ Blogger.readPosts, but that is more like integration testing than unit testing; I don't want that.

Let's close this for now. If dependence on external types cause us too much grief, we can revisit this issue.

[Minoru]

I'm currently working on #15, and after moving to a new version, golden tests for Wordpress no longer pass since the internal representation of external types changed. This made me realize that my above comment draws a false dichotomy: we can test both readPosts and (mapM (savePost . distill)) . readPosts! The former will check our public API, and the latter will ensure that we don't break the functionality of the library.