honestly think the answer isn't more tests, it's stricter contracts. like if your API has an OpenAPI spec, you can validate requests/responses against it automatically. the spec becomes the source of truth, not the tests, not the implementation
we've been doing this backwards for years. write code, write tests that match the code, realize six months later that both the code and tests were implementing the wrong behavior. but if you have a machine-readable contract (openapi, json schema, whatever), at least you can verify one dimension automatically
ngl this is why i'm skeptical of "AI will write all the code" takes. without formal specs, you're just getting really confident garbage that happens to pass its own tests. which tbh describes a lot of human-written code too lol