Flaky test: WaitsFor_Performance_Many_Quick_Polls times out on starved Windows CI runner #7325

What happened

WaitsFor_Performance_Many_Quick_Polls (tests/TUnit.Assertions.Tests/WaitsForAssertionTests.cs:249) failed on modularpipeline (windows-latest) for PR #7281 (a Renovate dependency bump that doesn't touch assertions code):

• Run: https://github.com/thomhurst/TUnit/actions/runs/41315148984/job/124873494863 (attempt 1, head 3150edca)
• TFM: net8.0

AssertionException: Expected assertion to pass within 5000 milliseconds (polling every 10ms)
but assertion did not pass within 5000ms after 18 attempts. Last error: Expected to be greater than 20

That failure aborted the pipeline, so PackTUnitFilesModule and the other modules show as cancelled (Attempting to cancel the build...). They were not real failures.

Cause

The test requires 21 polls at a 10 ms interval inside a 5 s timeout, and then requires the elapsed time to be under 5 s. Only 18 polls completed in 5 s, roughly 280 ms per poll, so the thread pool and timers on the runner were starved while the pipeline ran many test modules in parallel. The test measures wall-clock throughput on a shared CI machine rather than the behaviour of WaitsFor.

Expected

The test should check that WaitsFor keeps polling until the predicate passes, and it should not depend on runner speed. For example:

• use a generous timeout (e.g. 30 s) so the poll count is the only real condition, and
• drop or loosen the stopwatch.Elapsed < 5s assertion, which only measures CI load.

Earlier WaitsFor timing fixes: #6576, #7176 (and #7169).

Reproduce

Run TUnit.Assertions.Tests with --treenode-filter "/*/*/WaitsForAssertionTests/WaitsFor_Performance_Many_Quick_Polls" on a CPU-starved machine, e.g. with a parallel CPU stress load.