Quarantine ServerVirtualizationTest.AnchorMode_End_AppendAfterLeavingBottom_DoesNotReengage flaky test

[github-actions]

Failing Test(s)

• Microsoft.AspNetCore.Components.E2ETest.ServerExecutionTests.ServerVirtualizationTest.AnchorMode_End_AppendAfterLeavingBottom_DoesNotReengage

Symptoms

Assertion failure in scroll position check:

End mode: should not re-engage after leaving bottom. scrollTop before: 31320, after: 31940, scrollHeight before: 31620, after: 32240, clientHeight: 300

The test verifies that virtualization anchor mode does not re-engage after the user scrolls past the bottom. The scroll position check is flaky due to timing/race conditions in the scroll measurement.

Failing Builds

• https://dev.azure.com/dnceng-public/public/_build/results?buildId=1423868 (pipeline 87, main branch)
• https://dev.azure.com/dnceng-public/public/_build/results?buildId=1442108 (pipeline 87, merged PR)

Root Cause

Race condition in scroll position assertion — the virtualization component may re-measure scroll position before the DOM has fully settled, causing non-deterministic scroll state.

Generated by Daily Test Quarantine Management · sonnet46 11.1M · ◷

[github-actions]

Investigation

Failure pattern: The test asserts that the virtualization anchor mode (end-anchored scrolling) does not re-engage after the user scrolls past the bottom. The assertion fails intermittently when the scroll position measurements don't match expected values.

Error:

End mode: should not re-engage after leaving bottom.
scrollTop before: 31320, after: 31940
scrollHeight before: 31620, after: 32240
clientHeight: 300

The test expects scrollTop to remain stable after leaving the bottom boundary, but the DOM continues scrolling slightly — likely because the virtualization component is still rendering items as the scroll position changes, causing a feedback loop between DOM updates and scroll measurement.

Root cause assessment: Race condition between DOM rendering/measurement and scroll position checks. The ServerVirtualizationTest variant is particularly susceptible because server-side rendering introduces additional async rendering delays.

Builds:

• https://dev.azure.com/dnceng-public/public/_build/results?buildId=1423868
• https://dev.azure.com/dnceng-public/public/_build/results?buildId=1442108

Generated by Daily Test Quarantine Management · sonnet46 11.1M · ◷