Fix flaky mutants

[martincostello]

Fix flaky mutants after task refactoring in #2664.

[Copilot]

Pull Request Overview

This PR addresses flaky mutants in the Polly.Core circuit breaker controller by adding Stryker mutation testing exclusions. The changes disable mutation testing for specific conditional checks that are difficult to test reliably.

• Added Stryker disable comments for two conditional checks
• Prevents flaky mutation test failures for code paths that are hard to test deterministically

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 96.12%. Comparing base (0159145) to head (fc6b235).
⚠️ Report is 1 commits behind head on main.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2717   +/-   ##
=======================================
  Coverage   96.12%   96.12%           
=======================================
  Files         309      309           
  Lines        7118     7118           
  Branches     1008     1008           
=======================================
  Hits         6842     6842           
  Misses        222      222           
  Partials       54       54           

Flag	Coverage Δ
linux	96.12% <ø> (ø)
macos	96.12% <ø> (ø)
windows	96.11% <ø> (ø)

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[pentp]

Isn't the Debug.Assert(task.IsCompleted) assert below those conditions enough to fix the mutation tests? IIRC mutation tests always run in debug mode and those asserts should ensure that the opposite condition will fail, no?
If that's not the case, then some of the other Debug.Asserts I added might also be flaky.

[martincostello]

They are, but I've seen two different failing mutations since the merge.

Polly/eng/stryker-config.json

Line 23 in 0159145

"configuration": "Debug",

[pentp]

Oh, I think the reason is because Debug.Assert also gets mutated (removed) and if done together with the other mutation, then both will "survive". The reason I thought asserts would be enough is that in our codebase we have "ignore-methods": [ "Assert" ] in Stryker config and I had forgotten it's not the default.

[pentp]

This condition might also be flaky then:

Polly/src/Polly.Core/Hedging/Controller/HedgingExecutionContext.cs

Line 132 in 0159145

if (!whenAnyHedgedTask.IsCompleted)

Though I'm surprised that the similar condition below for if (completedTask == delayTask) doesn't seem to be flaky...

[martincostello]

I'd be happy to accept a PR to tweak our configuration to do the same and then revert these changes so the conditions are mutated again.

I'm going to merge this now though as 4-in-a-row failures in main and 3-in-a-row successes here suggests the flaky CI is at least resolved for now (🤞).

[pentp]

It's actually in the config already, so now I don't know why it was flaky:

Polly/eng/stryker-config.json

Line 15 in 0159145

"Debug.Assert",

[martincostello]

Just had another one happen here:

Polly/src/Polly.Core/Hedging/Controller/HedgingExecutionContext.cs

Line 132 in bb71bbe

if (!whenAnyHedgedTask.IsCompleted)

LogicalNotExpression to un-LogicalNotExpression mutation Survived (132:13)