Fix flaky BeLessThanOrEqualTo execution time test by Copilot · Pull Request #3200 · fluentassertions/fluentassertions

Copilot · 2026-04-23T12:18:10Z

Thread.Sleep(100) only guarantees a minimum sleep duration — on a loaded CI runner, the OS scheduler can delay wakeup well beyond 100ms, causing the 1-second limit to be exceeded intermittently.

Increase the BeLessThanOrEqualTo "should not throw" test limit from 1.Seconds() to 2.Seconds(), aligning it with the identical setup in the BeLessThan equivalent test which already uses that margin.

…limit Agent-Logs-Url: https://github.com/fluentassertions/fluentassertions/sessions/6963d932-6650-4e1b-9044-47692ab4a27f Co-authored-by: dennisdoomen <572734+dennisdoomen@users.noreply.github.com>

dennisdoomen

@copilot do a thorough investigation to see why this test is flaky. Is it the test itself or is it the implementation of the assertion API in FA

Copilot · 2026-04-23T12:38:27Z

@copilot do a thorough investigation to see why this test is flaky. Is it the test itself or is it the implementation of the assertion API in FA

Here's the full analysis:

The implementation is correct. The flakiness was entirely in the test.

How the timing path works

someAction.ExecutionTime() calls new ExecutionTime(action, createTimer) which immediately calls Task.Run(...). Inside that task, the action runs wrapped in a using (timer = createTimer()) block — the StopwatchTimer starts right before action() and stops (via Dispose) right after it completes.
BeLessThanOrEqualTo(maxDuration) calls PollUntil(duration => duration <= maxDuration, expectedResult: false, rate: maxDuration). For the success path with a 1-second limit:
- Initial check: elapsed ≈ 0, condition is 0 <= 1s = true, expectedResult is false → true == false → don't break early
- Calls execution.Task.Wait(1.Second()) — waits up to 1 second for the task to finish
- After the wait returns true, elapsed = execution.ElapsedTime reads the stopped stopwatch (stopped inside the task before IsRunning = false)
- Final check: elapsed <= maxDuration
Thread safety is sound: Task.Wait() provides the happens-before guarantee so that after it returns true, all writes from the task thread (including timer.Dispose() and IsRunning = false) are visible to the calling thread.

Why it was flaky

The StopwatchTimer measures actual wall-clock time inside the task, which includes:

Thread pool queue delay before the task starts running
The full actual duration of Thread.Sleep(100), which only guarantees a minimum sleep — on a loaded CI runner, the OS scheduler may not wake the thread for well over 100ms

With a 1-second limit and a 100ms sleep, there's nominally 900ms of slack. But under CI load, Thread.Sleep(100) can easily sleep for much longer, and if the measured elapsed time exceeds 1 second, the assertion fails.

Why the fix is correct

The equivalent BeLessThan test already used 2.Seconds() with the same Thread.Sleep(100) action. Aligning BeLessThanOrEqualTo to also use 2.Seconds() (20× the sleep duration) provides the same headroom and brings it in line with the sibling test's conventions. Fixed in c784841.

github-actions · 2026-04-23T13:18:23Z

Test Results

37 files ±0 37 suites ±0 2m 56s ⏱️ +20s
6 363 tests ±0 6 362 ✅ ±0 1 💤 ±0 0 ❌ ±0
39 524 runs ±0 39 518 ✅ ±0 6 💤 ±0 0 ❌ ±0

Results for commit c784841. ± Comparison against base commit 79050a9.

This pull request removes 10 and adds 8 tests. Note that renamed tests count towards both.

FluentAssertions.Specs.Streams.StreamAssertionSpecs+HaveLength ‑ When_a_throwing_stream_should_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HaveLength ‑ When_a_throwing_stream_should_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HavePosition ‑ When_a_throwing_stream_should_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HavePosition ‑ When_a_throwing_stream_should_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHaveLength ‑ When_a_throwing_stream_should_not_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHaveLength ‑ When_a_throwing_stream_should_not_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHavePosition ‑ When_a_throwing_stream_should_not_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHavePosition ‑ When_a_throwing_stream_should_not_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetLengthExceptionMessage'.)
Object name: 'GetPositionExceptionMessage'.)

FluentAssertions.Specs.Streams.StreamAssertionSpecs+HaveLength ‑ When_a_throwing_stream_should_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetLengthExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HaveLength ‑ When_a_throwing_stream_should_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetLengthExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HavePosition ‑ When_a_throwing_stream_should_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetPositionExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+HavePosition ‑ When_a_throwing_stream_should_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetPositionExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHaveLength ‑ When_a_throwing_stream_should_not_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetLengthExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHaveLength ‑ When_a_throwing_stream_should_not_have_a_length_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetLengthExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHavePosition ‑ When_a_throwing_stream_should_not_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetPositionExceptionMessage'.)
FluentAssertions.Specs.Streams.StreamAssertionSpecs+NotHavePosition ‑ When_a_throwing_stream_should_not_have_a_position_it_should_fail(exception: System.ObjectDisposedException: Cannot access a disposed object.
Object name: 'GetPositionExceptionMessage'.)

♻️ This comment has been updated with latest results.

coveralls · 2026-04-23T13:19:33Z

Coverage Report for CI Build 24835291706

Coverage remained the same at 97.172%

Details

Coverage remained the same as the base build.
Patch coverage: No coverable lines changed in this PR.
No coverage regressions found.

Uncovered Changes

No uncovered changes found.

Coverage Regressions

No coverage regressions found.

Coverage Stats


Relevant Lines:	13367
Covered Lines:	13142
Line Coverage:	98.32%
Relevant Branches:	4346
Covered Branches:	4070
Branch Coverage:	93.65%
Branches in Coverage %:	Yes
Coverage Strength:	66871.11 hits per line

💛 - Coveralls

github-actions · 2026-04-23T13:25:30Z

Qodana for .NET

It seems all right 👌

No new problems were found according to the checks applied

💡 Qodana analysis was run in the pull request mode: only the changed files were checked
☁️ View the detailed Qodana report

Contact Qodana team

Contact us at qodana-support@jetbrains.com

Or via our issue tracker: https://jb.gg/qodana-issue
Or share your feedback: https://jb.gg/qodana-discussions

Initial plan

22929d1

Copilot AI assigned Copilot and dennisdoomen Apr 23, 2026

Copilot started work on behalf of dennisdoomen April 23, 2026 12:18 View session

Copilot AI linked an issue Apr 23, 2026 that may be closed by this pull request

Test FluentAssertions.Specs.Specialized.ExecutionTimeAssertionsSpecs+BeLessThanOrEqualTo.When_the_execution_time_of_an_action_is_less_than_or_equal_to_a_limit_it_should_not_throw is flaky #3199

Closed

Fix flaky BeLessThanOrEqualTo execution time test by increasing time …

c784841

…limit Agent-Logs-Url: https://github.com/fluentassertions/fluentassertions/sessions/6963d932-6650-4e1b-9044-47692ab4a27f Co-authored-by: dennisdoomen <572734+dennisdoomen@users.noreply.github.com>

Copilot AI changed the title ~~[WIP] Fix flaky execution time assertions test~~ Fix flaky BeLessThanOrEqualTo execution time test Apr 23, 2026

Copilot finished work on behalf of dennisdoomen April 23, 2026 12:31

Copilot AI requested a review from dennisdoomen April 23, 2026 12:31

dennisdoomen requested changes Apr 23, 2026

View reviewed changes

Copilot started work on behalf of dennisdoomen April 23, 2026 12:34 View session

Copilot AI requested a review from dennisdoomen April 23, 2026 12:39

Copilot finished work on behalf of dennisdoomen April 23, 2026 12:39

dennisdoomen marked this pull request as ready for review April 23, 2026 14:04

dennisdoomen approved these changes Apr 23, 2026

View reviewed changes

dennisdoomen merged commit f1370c1 into main Apr 23, 2026
15 checks passed

dennisdoomen deleted the copilot/fix-flaky-execution-time-test branch April 23, 2026 14:07

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

Fix flaky BeLessThanOrEqualTo execution time test#3200

Fix flaky BeLessThanOrEqualTo execution time test#3200
dennisdoomen merged 2 commits into
mainfrom
copilot/fix-flaky-execution-time-test

Copilot AI commented Apr 23, 2026 •

edited

Loading

Uh oh!

dennisdoomen left a comment

Uh oh!

Copilot AI commented Apr 23, 2026

Uh oh!

github-actions Bot commented Apr 23, 2026 •

edited

Loading

Uh oh!

coveralls commented Apr 23, 2026 •

edited

Loading

Uh oh!

github-actions Bot commented Apr 23, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Uh oh!

Conversation

Copilot AI commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Uh oh!

dennisdoomen left a comment

Choose a reason for hiding this comment

Uh oh!

Copilot AI commented Apr 23, 2026

How the timing path works

Why it was flaky

Why the fix is correct

Uh oh!

github-actions Bot commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Test Results

Uh oh!

coveralls commented Apr 23, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

Coverage Report for CI Build 24835291706

Coverage remained the same at 97.172%

Details

Uncovered Changes

Coverage Regressions

Coverage Stats

💛 - Coveralls

Uh oh!

github-actions Bot commented Apr 23, 2026

Qodana for .NET

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

3 participants

Copilot AI commented Apr 23, 2026 •

edited

Loading

github-actions Bot commented Apr 23, 2026 •

edited

Loading

coveralls commented Apr 23, 2026 •

edited

Loading