One idea that @jorisvandenbossche suggested is that we should have a set of data that shows the range of the specification, that implementors can use to make sure they're handling right, and which could be the basis of 'integration' testing.

This would include geoparquet files that have a variety of projections, geometry types (including multiple geometry types as in #119), plus things like multiple geometry columns, different edges values, etc. It could also be good to have a set of 'bad' files that can also be tested against.