CI surfaced an Unhandled Error after the full vitest suite ran clean:
ReferenceError: ResizeObserver is not defined
at p (node_modules/@headlessui/react/dist/utils/element-movement.js:1:332)
at combobox-machine.js:1:8089
at y.send (machine.js:1:1383)
at Object.closeCombobox (combobox-machine.js:1:5820)
... originating from src/components/Combobox.test.tsx
Test Files 60 passed (60)
Tests 654 passed (654)
Errors 1 error ← vitest exits 1 on unhandled
Diagnosis
=========
Headless UI's Combobox + Dialog use ResizeObserver internally to
track trigger-element position (focus-management edge cases on
scroll / resize). jsdom does not implement ResizeObserver — without
a polyfill, Headless UI's async cleanup fires *after* the vitest
test completes (during the keyboard-nav close path) and throws the
ReferenceError as an Unhandled Error. The test assertions had
already passed; the unhandled exception alone causes vitest's
process exit to flip to 1.
Locally the error appeared as a "1 error" line below the green
summary but exit was still 0 because we ran with a tight timeout
that masked the post-test cleanup. The amd64 CI runner with the
full ~40s budget triggers the unhandled handler and propagates the
non-zero exit.
Fix
===
web/src/test/setup.ts adds a minimal ResizeObserverStub class
(observe / unobserve / disconnect are no-ops) and assigns it to
globalThis.ResizeObserver iff undefined. The component never reads
the observed dimensions in our test paths — the read sites fire
only after layout has settled in a real browser — so a no-op
construct + observer trio is sufficient to silence Headless UI's
internal calls.
Also stubs Element.prototype.scrollIntoView (Headless UI touches
it during Combobox.Options keyboard nav; jsdom warns rather than
throws but the CI log stays cleaner).
Verification
============
$ cd web && npx vitest run src/components/Combobox.test.tsx
Test Files 1 passed (1)
Tests 5 passed (5)
(no Unhandled Errors line; exit 0 — the post-test cleanup
no longer touches the undefined global)
$ cd web && npx tsc --noEmit
(exit 0)
This commit ships on top of Phase 1 (e37403ed). The 654-test
green-suite count is unchanged; only the post-suite cleanup
behaviour changes.
