Fix KeyNotFoundException in HttpRequestLatencyListener.OnEventWritten (#6823)

Author: pentp

test/Libraries/Microsoft.Extensions.Http.Diagnostics.Tests/Latency/Internal/HttpMockProvider.cs

@@ -40,7 +40,7 @@ public static Mock<ILatencyContext> GetLatencyContext()
         return lc;
     }
 
-    public class MockEventSource : EventSource
+    public class MockEventSource() : EventSource(throwOnEventWriteErrors: true)
     {
         public int OnEventInvoked;
 

test/Libraries/Microsoft.Extensions.Http.Diagnostics.Tests/Latency/Internal/HttpRequestLatencyListenerTest.cs

@@ -1,6 +1,7 @@
 // Licensed to the .NET Foundation under one or more agreements.
 // The .NET Foundation licenses this file to you under the MIT license.
 
+using System.Diagnostics.Tracing;
 using System.Linq;
 using Microsoft.Extensions.Diagnostics.Latency;
 using Microsoft.Extensions.Http.Latency.Internal;
@@ -84,8 +85,16 @@ public void HttpRequestLatencyListener_OnEventSourceCreated_NonHttpSources()
         listener.OnEventSourceCreated("test", es);
         Assert.Equal(0, es.OnEventInvoked);
         Assert.False(es.IsEnabled());
+
+        using var dummyListener = new DummyListener();
+        dummyListener.EnableEvents(es, EventLevel.LogAlways);
+
+        // EventSource seems to send the event to all listeners, even those that didn't enable the EventSource at all!
+        es.Write("Dummy");
     }
 
+    private sealed class DummyListener : EventListener;
+
     [Fact]
     public void HttpRequestLatencyListener_OnEventSourceCreated_HttpSources()
     {