Fable 5 Mode 4: Test-First Prompting
thisguyknowsai · x · 2026-07-03
While Fable 5 can write tests before implementation, it defaults to writing them after the code is done, much like most engineers. The author suggests reversing this: write the test suite based on specs first, then let Fable 5 run the tests and iterate until they pass, all without human intervention. This self-checking loop reportedly enabled an early user to compress a 50-million-line Ruby migration into a single day.
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