Bug 193091 – [ Mojave WK1 ] Four Layout Tests in fast/repaint/* are flaky

• Component: Tools / Tests
• Status: NEW

[Truitt Savell]

The following layout tests are flaky on Mojave WK1

fast/repaint/fixed.html
fast/repaint/fixed-to-relative-position-with-absolute-child.html
fast/repaint/fixed-scale.html
fast/repaint/absolute-position-changed.html

Probable cause:

These four image tests fail in tandem. All three tests seem to be drawing boxes, and incorrectly zooming in on the results. 

Flakiness Dashboard:

https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=fast%2Frepaint%2Ffixed.html%20fast%2Frepaint%2Ffixed-to-relative-position-with-absolute-child.html%20fast%2Frepaint%2Ffixed-scale.html%20fast%2Frepaint%2Fabsolute-position-changed.html

Links to image diffs:

fast/repaint/absolute-position-changed.html
https://build.webkit.org/results/Apple%20Mojave%20Release%20WK1%20(Tests)/r239577%20(1897)/fast/repaint/absolute-position-changed-diffs.html

fast/repaint/fixed-scale.html
https://build.webkit.org/results/Apple%20Mojave%20Release%20WK1%20(Tests)/r239577%20(1897)/fast/repaint/fixed-scale-diffs.html

fast/repaint/fixed-to-relative-position-with-absolute-child.html
https://build.webkit.org/results/Apple%20Mojave%20Release%20WK1%20(Tests)/r239577%20(1897)/fast/repaint/fixed-to-relative-position-with-absolute-child-diffs.html

fast/repaint/fixed.html
https://build.webkit.org/results/Apple%20Mojave%20Release%20WK1%20(Tests)/r239577%20(1897)/fast/repaint/fixed-diffs.html

[Ryan Haddad]

The symptoms here look very similar to https://bugs.webkit.org/show_bug.cgi?id=192881, where the "actual" image is blank white.

[Truitt Savell]

I have been unable to reproduce the failures with either running the four tests continuously, running the whole directory repeatedly on one process, or by running the single test runner they all fail on in one process.