Function check_upcasting 

pub async fn check_upcasting(fresh: UpcastingFactory<'_>, older: &str) -> Report

Run the checks that need a store built with an upcaster.

older is an export one record shape older than this build writes, as older_shape crafts it; no build can write one, so the battery is handed it rather than producing it.

Panics

Only if the factory itself fails.