Agent shipped 10 features in a day, all 374 tests green — the page didn't render
Sinjared · reddit · 2026-09-09
A developer's coding agent merged 10 UI features into a daily-use web console; all 374 tests across 11 suites passed, yet the page was unusable — one section rendered as an 88px-wide, 2452px-tall column. Root cause: three lines of CSS. The stylesheet defined span-3/4/6/8 but never span-12, and the JS applied span-12 to 24 elements, all falling back to 1/12 of a twelve-column grid. None of the tests asserted computed layout — jsdom doesn't compute grid at all. The lesson: agent verification only covers what someone thought to encode, and 'does this look right' is never tested. The author's stopgap is a headless-browser check that walks every view and fails on wrong grid spans and horizontal overflow, but wonders if something better already exists.
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