[PROJECT IDEA] IATI "Data tests" repo

[stevieflow]

Rationale

It's difficult to follow the exact Rulesets that are official to the standard,vs those that are in place for tools such as the validator

Getting beyond the concept of "rules" would be useful, as they can often be context-specific and conditional

It'd therefore be useful to house rules as "tests" in a single repo, and then annotate their relevance and use

This repo could also be used to formulate new tests

Users could then integrate relevant tests into their applications (possibly through a library...)

Proposal

There's a bunch of rules and tests already in existence - this would be about pulling them into one place, and annotating (which is not an easy task, admittedly)