Fix race condition in UnreliableL2Tests.WriteFailureInvisible

[Copilot]

The test was intermittently failing in CI because L2 write failures are logged asynchronously after the background write task completes, but the test used a fixed 150ms delay that didn't reliably wait for logging to finish.

Changes

• LogCollector: Added WaitForLogsAsync that polls for expected log entries with timeout instead of guessing timing
• UnreliableL2Tests: Replaced fixed delay with WaitForLogsAsync(errorIds, TimeSpan.FromSeconds(5))

The polling logic matches AssertErrors exactly (count and order must match), ensuring test assertions see the same log state that will be verified.

// Before: unreliable fixed delay
await l2.LastWrite;
await Task.Delay(150); // thread jitter caused failures
log.AssertErrors(errorIds);

// After: poll until logs appear or timeout
await l2.LastWrite;
await log.WaitForLogsAsync(errorIds, TimeSpan.FromSeconds(5));
log.AssertErrors(errorIds);

Original prompt

This test failed in CI. Please either investigate the flakiness and fix it, or disable the test if it's inherently flaky:

Microsoft.Extensions.Caching.Hybrid.Tests.UnreliableL2Tests.WriteFailureInvisible(writeBreak: AsynchronousYield, errorIds: [7])

Result Details
Failed 39m ago on 642af2e5c000000
Duration0:00:00.673
Ownernot available
Date started11/21/2025, 9:29:23 AM
Date completed11/21/2025, 9:29:24 AM
Failing since37m ago
Failing since build20251121.17

Debug

Work items

Attachments

History

1ES Test Attachments

Artifacts

Error message
Assert.Equal() Failure: Strings differ
↓ (pos 0)
Expected: "7"
Actual: ""

Stack trace
at Microsoft.Extensions.Caching.Hybrid.Tests.LogCollector.AssertErrors(Int32[] errorIds) in /mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.Caching.Hybrid.Tests/LogCollector.cs:line 60
at Microsoft.Extensions.Caching.Hybrid.Tests.UnreliableL2Tests.WriteFailureInvisible(BreakType writeBreak, Int32[] errorIds) in /mnt/vss/_work/1/s/test/Libraries/Microsoft.Extensions.Caching.Hybrid.Tests/UnreliableL2Tests.cs:line 49
--- End of stack trace from previous location ---

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Microsoft Reviewers: Open in CodeFlow

[Copilot]

Pull request overview

This PR fixes a flaky test (WriteFailureInvisible) that was intermittently failing in CI due to a race condition. The test verifies that L2 cache write failures are properly logged, but because these failures are logged asynchronously after a background write task completes, the original fixed 150ms delay was insufficient to reliably wait for logging to finish.

Key Changes:

• Added WaitForLogsAsync method to LogCollector that polls for expected log entries with a timeout instead of using fixed delays
• Updated WriteFailureInvisible test to use WaitForLogsAsync(errorIds, TimeSpan.FromSeconds(5)) instead of Task.Delay(150)

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
test/Libraries/Microsoft.Extensions.Caching.Hybrid.Tests/LogCollector.cs	Added WaitForLogsAsync method that polls for log entries matching expected error IDs with configurable timeout, using thread-safe lock-based checking that mirrors the validation logic in AssertErrors
test/Libraries/Microsoft.Extensions.Caching.Hybrid.Tests/UnreliableL2Tests.cs	Replaced unreliable fixed 150ms delay with WaitForLogsAsync call that polls for up to 5 seconds, ensuring logs are present before assertion

[ericstj]

Looks good, just had a question that might simplify the method.