Module testing framework / example data

[makkus]

I'd like to have example data for each module we write (where applicable -- for some module it might not make sense), and some conventions on where to store it. An obvious place would be the same repo as the module code (maybe under data/<module_name> or so), or a seperate repo with the same name and a -data prefix.

That data then is used as input for automated tests, as well as linked from auto-generated documentation pages for each module, so users can use the data to play with modules without having to find the data to do so themselves.