Took me a bit, but finally got around to checking this out!
This is a great talk, love it! Really appreciate the callout about using public interfaces for test setup across packages, rather than using factory bot (private API) for test setup. It feels like in practice this is an unpopular opinion, but I feel like it’s a really valuable concept for preserving boundaries. Personally I even like the (more unpopular) idea of even having within-package tests only test the public APIs (i.e. “unit test” by exercising edge cases handled by a private implementor through the public interface).