Flaky RenderTarget test

[pmconne]

Describe the bug The following test failure in core-full-stack-tests occasionally occurs in CI jobs.

1) RenderTarget
       should override symbology:

      AssertionError: expected 4 to equal 2
      + expected - actual

      -4
      +2

      at D:/vsts_a/279/s/full-stack-tests/core/src/frontend/standalone/RenderTarget.test.ts:368:32
      at testOnScreenViewport (D:/vsts_a/279/s/full-stack-tests/core/src/frontend/TestViewport.ts:336:5)
      at testViewports (D:/vsts_a/279/s/full-stack-tests/core/src/frontend/TestViewport.ts:360:3)
      at testViewportsWithDpr (D:/vsts_a/279/s/full-stack-tests/core/src/frontend/TestViewport.ts:368:5)
      at Context.<anonymous> (D:/vsts_a/279/s/full-stack-tests/core/src/frontend/standalone/RenderTarget.test.ts:264:5)

To Reproduce Submit PR. See if failure above occurs.

Expected behavior Test should pass consistently.

Desktop (please complete the applicable information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]
• iTwin.js Version [e.g. 2.5.3] master

Additional context Most recent occurrence was in #4414. Seems to have begun occurring maybe 1-2 months prior?

The specific "actual" value reported seems to differ from one failing run to the next.

[pmconne]

@markschlosseratbentley might this have coincided with your switching the tests to use waitForSceneCompletion?

[markschlosseratbentley]

@markschlosseratbentley might this have coincided with your switching the tests to use waitForSceneCompletion?

@pmconne A specific test -- WaitForSceneCompletion.test.ts -- was added to exercise the waitForSceneCompletion API. The rest of the tests all should still be using whatever their pre-existing wait logic entailed.

[pmconne]

Seems to only occur on Windows.

[markschlosseratbentley]

This is not reproducible so far locally. @markschlosseratbentley try on Windows.

[markschlosseratbentley]

Check if skipped. Consider priority then.

[markschlosseratbentley]

Test is skipped; moving to Proposed so time can be spent looking at higher priority flaky tests.