document testing story

[rbtcollins]

pest_consume doesn't include any testing support macros; its not clear what the best / typical practice is - to write tests on top of the high level API, or to derive a second struct from the same grammar with pest_derive and use pest macros to do unit testing of that grammar...

[Nadrieril]

Hm, I never considered unit testing a grammar but that sounds useful. I don't have a use for it so I won't write it myself, but I'd welcome a contribution of some simple testing macros

[spencerpogo]

Personally, I pass in inputs and then assert that they produce a certain AST or error in a certain way and it works for me.