The CLI is presently being reworked to expose that capability. Right now, you can use FunctionTest in order to validate that you get your expected outputs from an input. This works well because you can test many scenarios, including error conditions. The CLI does not currently emit the materialized manifests purely because our initial use cases needed to map values from reconciled manifests into other manifests. It is completely viable to emit the materialized manifests though.
Honestly, our ambition is to develop a tool that makes the operations and platform engineering people's lives better. Our team is comprised of software engineers who've worked in the operations and platform engineering space for a long time. It is a crowded space for sure, but I am optimistic, probably foolishly so, that we can develop something that is more pleasant for the platform folks than many of the other options.
We'd welcome any other feedback or thoughts on how to accomplish that.