Here's a link to the Production Acceptance Procedures for the RV-12. Although it's RV-12 specific, it's probably a pretty good guide for any homebuilder.
https://www.vansaircraft.com/wp-content/uploads/2020/10/RV-12-Production-Acceptance-Procedures-R14.pdf
There is a fuel system flow test on page G4-1. Under the system in the USA Vans is the registered builder of an ELSA RV-12, not the actual builder, so they need evidence that all the tests have been completed.