This looks so very cool, and so then all the more thought provoking that the tests themselves are closed-source, unlike the rest of the codebase. In this evolving world of rapidly improving llm coding agent productivity, the idea that the tests are more important than the implementation starts to ring true.
I was thinking about sqlite's test landscape as described here, in relation to simonw's recent writing about porting/recreating the justHTML engine from python to js via codex, nearly "automatically" with just a prompt and light steering.
SQLite's HowSQLiteIsTested reads like a bible of testing. I've know few who score merely highly by comparison
It's made a lot of sense in general if you think about the business models around open source products. An extensive test suite gives you the ability to engineer changes effectively and efficiently, meaning that you can also add additional value on top of released versions better than everyone else.