Repro Test for #3720 (Unobserved Exception)

[benrr101]

Description

This PR provides a reliable reproduction of #3720 in which an exception produced by the AsyncIOCompletionCallback of the SNI Packet class is not observed, leading to the unobserved exception handler being invoked.

This PR does not attempt to fix the issue, just adds a test that can be used to verify that the behavior exists. Attempts to fix the issue will inherently break this test, but can easily be fixed by changing the single assert in the test from "IsNotNull" to "IsNull".

Issues

#3720

Testing

Ran for hundreds of iterations with no failures observed.

[Copilot]

Pull request overview

Adds unit-test infrastructure and a targeted repro test for issue #3720, demonstrating that exceptions thrown from SniPacket’s async IO completion callback can go unobserved and later surface via TaskScheduler.UnobservedTaskException.

Changes:

• Introduces a shared ObservableException test utility to uniquely tag unobserved exceptions.
• Refactors AsyncHelperTest to use the shared ObservableException instead of an inline nested type.
• Adds a new Managed SNI unit test that reliably reproduces the unobserved-exception behavior.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 5 comments.

File	Description
src/Microsoft.Data.SqlClient/tests/UnitTests/Utilities/ObservableException.cs	Adds a reusable exception type for unobserved-exception testing scenarios.
src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlClient/Utilities/AsyncHelperTest.cs	Removes the inline ObservableException in favor of the shared utility type.
src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlClient/ManagedSni/SniPacketAsyncCallbackTest.cs	Adds a repro test for unobserved exceptions originating from SniPacket async callbacks.

[paulmedynski]

Blocking on Copilot feedback. My suggestion about ObservableException is at your discretion.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

Comments suppressed due to low confidence (1)

src/Microsoft.Data.SqlClient/tests/UnitTests/Microsoft/Data/SqlClient/ManagedSni/SniPacketTests.cs:47

• The unobserved-exception filter is currently using InnerExceptions.Contains(testException), which relies on reference equality. This makes the test more brittle and also diverges from the ObservableException remarks and existing AsyncHelperTest pattern (match by Identifier). Consider matching ObservableException.Identifier instead (without LINQ, per prior discussion).

            EventHandler<UnobservedTaskExceptionEventArgs> handleUnobservedException =
                (_, args) =>
                {
                    if (args.Exception.InnerExceptions.Contains(testException))
                    {
                        args.SetObserved();
                        unobservedExceptionRaised.TrySetResult(args.Exception);
                    }
                };

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.59%. Comparing base (fdebcd2) to head (de23155).
⚠️ Report is 33 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4460      +/-   ##
==========================================
- Coverage   65.83%   62.59%   -3.25%     
==========================================
  Files         287      283       -4     
  Lines       43763    67285   +23522     
==========================================
+ Hits        28812    42114   +13302     
- Misses      14951    25171   +10220     

Flag	Coverage Δ
CI-SqlClient	?
PR-SqlClient-Project	62.59% <ø> (?)

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[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated no new comments.