Fix r10 tabs test

[AndrewMusgrave]

WHY are these changes introduced?

Fixes #2694

WHAT is this pull request doing?

Removing the setTimeout mock

How to 🎩

1. git reset HEAD~2 --hard
2. dev up # or yarn install
3. yarn test TabMeasurer

[github-actions]

🟢 No significant changes to src/**/*.tsx were detected.

[BPScott]

This fixes the tests but I'm worried that this is just fixing a symptom rather than a root cause. I'm curious about why we need that setTimeout call in the first place - and why only in development mode?

Some folks appear to be having problems on the initial render - see the comment on the original issue and https://discourse.shopify.io/t/reloading-ssr-application-causes-polaris-tabs-to-load-differently/6389.

Perhaps the measurement handling should be done with a useLayoutEffect rather than useEffect? (which will need to be wrapped in some custom hook because it doesn't play nice with SSR)

[AndrewMusgrave]

This fixes the tests but I'm worried that this is just fixing a symptom rather than a root cause. I'm curious about why we need that setTimeout call in the first place - and why only in development mode?

I'm not sure. IIRC at one point in time, styles loading was delayed. Just a shot in the dark but they may have been needed for measuring.

Some folks appear to be having problems on the initial render - see the comment on the original issue and https://discourse.shopify.io/t/reloading-ssr-application-causes-polaris-tabs-to-load-differently/6389.

@dleroux Mentioned we've had this issue for a while, so I don't think it's related to the react bump.

Perhaps the measurement handling should be done with a useLayoutEffect rather than useEffect? (which will need to be wrapped in some custom hook because it doesn't play nice with SSR)

If we do need to delay measurements, in production that would be the way to go 👍 However I don't think that'll fix the test. React uses setTimeout in their scheduler and I'm betting our mock breaks it 😄

[AndrewMusgrave]

For reference plus created an issue #2706