Bug 310211 – [macOS] imported/w3c/web-platform-tests/webvtt/rendering/cues-with-video/processing-model/selectors/cue/background_shorthand_css_relative_url.html is a flaky image diff

• Status: NEW
• Component: New Bugs

[Diego De La Toba]

imported/w3c/web-platform-tests/webvtt/rendering/cues-with-video/processing-model/selectors/cue/background_shorthand_css_relative_url.html is a flaky image diff on macOS


HISTORY:
https://results.webkit.org/?suite=layout-tests&test=imported%2Fw3c%2Fweb-platform-tests%2Fwebvtt%2Frendering%2Fcues-with-video%2Fprocessing-model%2Fselectors%2Fcue%2Fbackground_shorthand_css_relative_url.html


DIFF:
https://build.webkit.org/results/Apple-Tahoe-Debug-AppleSilicon-WK2-Tests/309478@main%20(1348)/imported/w3c/web-platform-tests/webvtt/rendering/cues-with-video/processing-model/selectors/cue/background_shorthand_css_relative_url-diffs.html


IMAGES:
See attached.


REPRODUCTION:
I was able to reproduce this on macOS Tahoe Release and Debug with the following:

run-webkit-tests --no-build --no-retry --no-show-results --exit-after-n-failures=1 --expect-pass --iterations=469 --force -f --debug imported/w3c/web-platform-tests/webvtt/rendering/cues-with-video/processing-model/selectors/cue/background_shorthand_css_relative_url.html

I am going to mark expectations as imageOnlyFailure Pass while this pends investigation

[Radar WebKit Bug Importer]

<rdar://problem/172860387>

[Diego De La Toba]

Test gardening pull request: https://github.com/WebKit/WebKit/pull/60882

[EWS]

Test gardening commit 309501@main (ca7657d68d24): <https://commits.webkit.org/309501@main>

Reviewed commits have been landed. Closing PR #60882 and removing active labels.

[Diego De La Toba]

The test is flaky because the onplaying event handler called takeScreenshot() immediately after pausing the video. This results in a blank screenshot (no cue text visible) compared against the reference that always shows the text due to video rendering times being slower on debug and release builds under load. The fix is to add a 10ms delay before the screenshot.

[Diego De La Toba]

Pull request: https://github.com/WebKit/WebKit/pull/60886