[Webkit-unassigned] [Bug 195969] New: [ Mac WK2 ] Layout Test js/dom/unhandled-promise-rejection-bindings-type-error.html is a flaky failure

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=195969

            Bug ID: 195969
           Summary: [ Mac WK2 ] Layout Test
                    js/dom/unhandled-promise-rejection-bindings-type-error
                    .html is a flaky failure
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: Tools / Tests
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: sroberts at apple.com
                CC: lforschler at apple.com

The following layout test is failing on Mac WK2

js/dom/unhandled-promise-rejection-bindings-type-error.html

Probable cause:

Just showed up on the dashboard for the first time around r243141. Cannot find a regression point as I got it to fail locally with the oldest builds I could spade of Mojave Release WK2(228049) and Mojave Debug WK2(230024) . 
I could get it to fail consistently once I added -gf to my repro steps, and it would fail usually 2 within 10 tries. I could also get it to fail when running without it, but maybe 1 or 2 times in 10000 iterations. I get the same diff locally as seen on the server error. 

Reproduced with :

run-webkit-tests js/dom/unhandled-promise-rejection-bindings-type-error.html -gf --iterations 2500 --exit-after-n-failures=2 --no-retry
run-webkit-tests js/dom/unhandled-promise-rejection-bindings-type-error.html -gf --iterations 2500 --debug --exit-after-n-failures=2 --no-retry

Flakiness Dashboard:

https://webkit-test-results.webkit.org/dashboards/flakiness_dashboard.html#showAllRuns=true&tests=js%2Fdom%2Funhandled-promise-rejection-bindings-type-error.html

Diff:

--- /Volumes/Data/slave/mojave-debug-tests-wk2/build/layout-test-results/js/dom/unhandled-promise-rejection-bindings-type-error-expected.txt
+++ /Volumes/Data/slave/mojave-debug-tests-wk2/build/layout-test-results/js/dom/unhandled-promise-rejection-bindings-type-error-actual.txt
@@ -1,10 +1,7 @@
-CONSOLE MESSAGE: Unhandled Promise Rejection: TypeError: The PromiseRejectionEvent.promise getter can only be used on instances of PromiseRejectionEvent
 Test rejected promises are returned from bindings and trigger unhandledrejection.

 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".

-PASS error.promise is promise
-PASS error.reason instanceof TypeError is true
 PASS successfullyParsed is true

 TEST COMPLETE

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