Fix flaky OutgoingFilter_MultipleFilters_ExecuteInOrder test (#1488)

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: ericstj

tests/ModelContextProtocol.AspNetCore.Tests/MapMcpTests.cs

@@ -5,6 +5,7 @@
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol;
 using ModelContextProtocol.Server;
+using ModelContextProtocol.Tests.Utils;
 using System.ComponentModel;
 using System.Diagnostics;
 using System.Net;
@@ -394,6 +395,7 @@ await client.CallToolAsync("sampling-tool",
     public async Task OutgoingFilter_MultipleFilters_ExecuteInOrder()
     {
         var executionOrder = new List<string>();
+        var allFiltersComplete = new TaskCompletionSource(TaskCreationOptions.RunContinuationsAsynchronously);
 
         Builder.Services.AddMcpServer()
             .WithHttpTransport(ConfigureStateless)
@@ -411,6 +413,7 @@ public async Task OutgoingFilter_MultipleFilters_ExecuteInOrder()
                     if (context.JsonRpcMessage is JsonRpcResponse r2 && r2.Result is JsonObject obj2 && obj2.ContainsKey("tools"))
                     {
                         executionOrder.Add("filter1-after");
+                        allFiltersComplete.TrySetResult();
                     }
                 });
 
@@ -439,6 +442,14 @@ public async Task OutgoingFilter_MultipleFilters_ExecuteInOrder()
 
         await client.ListToolsAsync(cancellationToken: TestContext.Current.CancellationToken);
 
+        // The outermost filter's "after" callback runs after the response has been
+        // sent to the client, so ListToolsAsync may return before it executes.
+        // Wait for it to complete before asserting, but use a timeout to avoid hanging
+        // the test indefinitely if the filter pipeline regresses.
+        using var allFiltersCts = CancellationTokenSource.CreateLinkedTokenSource(TestContext.Current.CancellationToken);
+        allFiltersCts.CancelAfter(TestConstants.DefaultTimeout);
+        await allFiltersComplete.Task.WaitAsync(allFiltersCts.Token);
+
         Assert.Equal(["filter1-before", "filter2-before", "filter2-after", "filter1-after"], executionOrder);
     }