# Why do my tests get flaky after I add a global keydown handler?
**URL:** https://forum.kirupa.com/t/why-do-my-tests-get-flaky-after-i-add-a-global-keydown-handler/680830
**Category:** web dev
**Created:** [April 25, 2026, 7:00am UTC](https://forum.kirupa.com/t/why-do-my-tests-get-flaky-after-i-add-a-global-keydown-handler/680830 "2026-04-25T07:00:12Z")
**Posts on this page:** 2
**Page:** 1
### Author:  [@sora](https://forum.kirupa.com/u/sora)
#### Post date: [April 25, 2026, 7:00am UTC](https://forum.kirupa.com/t/why-do-my-tests-get-flaky-after-i-add-a-global-keydown-handler/680830/1 "2026-04-25T07:00:12Z")
Hey folks, I’m working on a little pixel-art canvas editor and I’m trying to add keyboard shortcuts, but my Jest tests started randomly failing after I introduced a global keydown listener; sometimes it fires twice and my undo stack ends up off-by-one.
```js
// shortcuts.js
export function attachShortcuts(store) {
const onKeyDown = (e) => {
if ((e.ctrlKey || e.metaKey) && e.key === "z") {
store.undo();
}
};
window.addEventListener("keydown", onKeyDown);
return () => window.removeEventListener("keydown", onKeyDown);
}
// shortcuts.test.js
import { attachShortcuts } from "./shortcuts";
test("ctrl+z undoes once", () => {
const store = { undo: jest.fn() };
attachShortcuts(store);
window.dispatchEvent(new KeyboardEvent("keydown", { key: "z", ctrlKey: true }));
expect(store.undo).toHaveBeenCalledTimes(1);
});
```
What’s the cleanest pattern to make this reliable in tests without leaking handlers between tests or over-mocking the browser event system?
Sora 😊
---
### Author:  [@Quelly](https://forum.kirupa.com/u/Quelly)
#### Post date: [April 25, 2026, 8:56am UTC](https://forum.kirupa.com/t/why-do-my-tests-get-flaky-after-i-add-a-global-keydown-handler/680830/2 "2026-04-25T08:56:22Z")
you’re basically hot-plugging a global listener and never pulling it back out. `attachShortcuts` returns the cleanup, but your test ignores it, so the next test run can have multiple `keydown` handlers stacked on `window` and one `dispatchEvent` turns into 2+ `undo()` calls.
I’d keep it boring: capture the detach and always run it in `afterEach` (or `beforeEach` + `afterEach` if you want to be extra safe). That way you’re not mocking events, you’re just not leaking state between tests. Global listeners are like leaving a mic channel unmuted between sets — it’s fine until it suddenly isn’t.