Reduce Allocation when choosing the Destination

[Kahbazi]

#174 (comment)

[Tratcher]

Tests are failing with a stack overflow?

   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparerAdapter`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.Object, System.Object)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].CheckIfEnumerablesAreEqual(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparerAdapter`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.Object, System.Object)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].CheckIfEnumerablesAreEqual(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparerAdapter`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.Object, System.Object)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].CheckIfEnumerablesAreEqual(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Assert.Equal[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.__Canon, System.__Canon, System.Collections.Generic.IEqualityComparer`1<System.__Canon>)
   at Xunit.Assert.Equal[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.__Canon, System.__Canon)
   at Microsoft.ReverseProxy.Service.Proxy.Tests.LoadBalancerTests.PickDestination_SingleDestinations_ShortCircuit()

reverse-proxy/test/ReverseProxy.Tests/Service/Proxy/LoadBalancerTests.cs

Lines 47 to 49 in 86f9c12

	var result = loadBalancer.PickDestination(destinations, in options);
	Assert.Equal(result, destinations[0]);

XUnit can't seem to figure out if it should compare these as objects or lists. I don't think there's anything wrong with your implementation, this might just be that the complier is defaulting var result to IReadOnlyList for lack of a more specific restraint. Try updating the test?

[halter73]

Now DynamicState_WithHealthChecks_HonorsHealthState is failing with a stack overflow.

It seems XUnit's Assert.Equal really doesn't play nice with lists that return themselves as a list item. It just keeps recursively enumerating what it sees as an infinitely nested list. Anything that tries to call Assert.Equal on a DestinationInfo or anything containing a DestinationInfo will fail this way.

Stack overflow.
   at System.Linq.Enumerable.Where[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.Collections.Generic.IEnumerable`1<System.__Canon>, System.Func`2<System.__Canon,Boolean>)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].IsSet(System.Reflection.TypeInfo)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].CheckIfSetsAreEqual(System.__Canon, System.__Canon, System.Reflection.TypeInfo)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparerAdapter`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.Object, System.Object)
...
   at Xunit.Sdk.AssertEqualityComparerAdapter`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.Object, System.Object)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].CheckIfEnumerablesAreEqual(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparerAdapter`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.Object, System.Object)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].CheckIfEnumerablesAreEqual(System.__Canon, System.__Canon)
   at Xunit.Sdk.AssertEqualityComparer`1[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]].Equals(System.__Canon, System.__Canon)
   at Xunit.Assert.Equal[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.__Canon, System.__Canon, System.Collections.Generic.IEqualityComparer`1<System.__Canon>)
   at Xunit.Assert.Equal[[System.__Canon, System.Private.CoreLib, Version=5.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]](System.__Canon, System.__Canon)
   at Microsoft.ReverseProxy.RuntimeModel.Tests.BackendInfoTests.DynamicState_WithHealthChecks_HonorsHealthState()

@Kahbazi If you click the "View more details on Azure Pipelines" link at the bottom of this PR's "Checks" tab, you should be able to see the test failure details by downloading the "2 published" artifacts. We still need to fix things so test failures are properly reported. @Tratcher Is there already an issue tracking improving the test failure output in PR checks?

It is nice that stack overflows finally show stack traces though! dotnet/runtime#31956

[Tratcher]

Is there already an issue tracking improving the test failure output in PR checks?

I had assumed the test reporting was bad in this case because of the StackOverflow. I can try it with a more typical error in another PR.

[Tratcher]

Yeah, normal test failures work. StackOveflow is special.
https://dev.azure.com/dnceng/public/_build/results?buildId=664478&view=ms.vss-test-web.build-test-results-tab&runId=20601422&resultId=100187&paneView=debug

[Tratcher]

Thanks