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.

[paulmedynski]

Should this class generate its own GUID? Not sure it needs one injected, or that it needs a setter:

public class ObservableException : Exception
{
  public Guid Identifier { get; } = new();
}

[paulmedynski]

I guess there is one existing use of this class, but it could be esaily re-arranged to work with the above.

I generally try to avoid providing any unnecessary API surface.

[benrr101]

I have a bit of a grander idea for it ... so I might omit this change for now 😬

[benrr101]

Ok, scope creep time, I turned the structure of the observable exception testing into a disposable helper that takes care of its own setup and cleanup. This also consolidates the flakiness hardening into one spot. The async helper tests have been updated to use this (and as a result the tests take longer, but it is robust to flakiness - within reason).

[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 64.87%. Comparing base (fdebcd2) to head (f39f395).
⚠️ Report is 23 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4460      +/-   ##
==========================================
- Coverage   65.83%   64.87%   -0.96%     
==========================================
  Files         287      287              
  Lines       43763    66958   +23195     
==========================================
+ Hits        28812    43440   +14628     
- Misses      14951    23518    +8567     

Flag	Coverage Δ
CI-SqlClient	?
PR-SqlClient-Project	64.87% <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.