Revert to original DisableParallelization collection, remove Activity.Current and ForceFlush changes

Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>

Author: Copilot

tests/ModelContextProtocol.Tests/DiagnosticTests.cs

@@ -9,15 +9,12 @@
 
 namespace ModelContextProtocol.Tests;
 
-[Collection(nameof(ExclusiveExecution))]
+[Collection(nameof(DisableParallelization))]
 public class DiagnosticTests
 {
     [Fact]
     public async Task Session_TracksActivities()
     {
-        // Ensure no ambient activity from previous tests
-        Activity.Current = null;
-
         var activities = new List<Activity>();
         var clientToServerLog = new List<string>();
 
@@ -35,9 +32,6 @@ await RunConnected(async (client, server) =>
                 var tool = tools.First(t => t.Name == "DoubleValue");
                 await tool.InvokeAsync(new() { ["amount"] = 42 }, TestContext.Current.CancellationToken);
             }, clientToServerLog);
-
-            // Ensure all activities are flushed before disposal
-            tracerProvider.ForceFlush();
         }
 
         Assert.NotEmpty(activities);
@@ -83,9 +77,6 @@ await RunConnected(async (client, server) =>
     [Fact]
     public async Task Session_FailedToolCall()
     {
-        // Ensure no ambient activity from previous tests
-        Activity.Current = null;
-
         var activities = new List<Activity>();
 
         using (var tracerProvider = OpenTelemetry.Sdk.CreateTracerProviderBuilder()
@@ -98,9 +89,6 @@ await RunConnected(async (client, server) =>
                 await client.CallToolAsync("Throw", cancellationToken: TestContext.Current.CancellationToken);
                 await Assert.ThrowsAsync<McpProtocolException>(async () => await client.CallToolAsync("does-not-exist", cancellationToken: TestContext.Current.CancellationToken));
             }, []);
-
-            // Ensure all activities are flushed before disposal
-            tracerProvider.ForceFlush();
         }
 
         Assert.NotEmpty(activities);

tests/ModelContextProtocol.Tests/TestAttributes.cs

@@ -1,32 +1,9 @@
-/// <summary>
-/// Test collection for tests that require exclusive execution (no parallel execution with any other tests).
-/// This is needed for tests that interact with global static state like ActivitySource in OpenTelemetry.
-/// </summary>
-/// <remarks>
-/// The fixture ensures mutual exclusion across ALL tests by using a static semaphore.
-/// Tests in this collection will acquire the semaphore before running and release it after,
-/// preventing any other test from running concurrently.
-/// </remarks>
-[CollectionDefinition(nameof(ExclusiveExecution))]
-public sealed class ExclusiveExecution : ICollectionFixture<ExclusiveExecutionFixture>;
+// Uncomment to disable parallel test execution for the whole assembly
+//[assembly: CollectionBehavior(DisableTestParallelization = true)]
 
 /// <summary>
-/// Fixture that ensures only one test runs at a time across the entire test assembly.
+/// Enables test classes to individually be attributed as [Collection(nameof(DisableParallelization))]
+/// to have those tests run non-concurrently with any other tests.
 /// </summary>
-public sealed class ExclusiveExecutionFixture : IAsyncLifetime
-{
-    private static readonly SemaphoreSlim s_exclusiveLock = new(1, 1);
-
-    public async ValueTask InitializeAsync()
-    {
-        // Acquire the lock before any test in this collection starts
-        await s_exclusiveLock.WaitAsync();
-    }
-
-    public ValueTask DisposeAsync()
-    {
-        // Release the lock after the test completes
-        s_exclusiveLock.Release();
-        return default;
-    }
-}
+[CollectionDefinition(nameof(DisableParallelization), DisableParallelization = true)]
+public sealed class DisableParallelization;