Will, it depends on the AI. Anthropic used to have a lecture-length system prompt for their models to explain this stuff—part of the secret sauce for Claude Code—and famously found that the 5 series models no longer need it.

As usual, if you use anything but the best model available I’m going to state that the better ones do better. If you do use the best model available, then I’ll just mention that Fable still has limits and still needs some guidance.

One thing it does not do is deliberately build tests which test nothing at all, or which restate the code under test. I mention this because certain other models absolutely would.