> I’m going to add a recommendation in our docs for pgtestdb, particularly for users aiming to test end-to-end (i.e. job inserted by client → fully completed by worker).

That's exactly what I did to learn River — implementing simple apps and testing their execution with pgtestdb: https://github.com/lukasschwab/river-playground

The starter skeleton was LLM-generated and not quite perfect, but discovering the coding agent's mistakes was satisfying in its own right.