fix: serialize MTP server-mode concurrent sessions to prevent stochastic 0-result runs

TUnit.Core/Models/GlobalContext.cs

@@ -6,16 +6,17 @@ namespace TUnit.Core;
 
 public class GlobalContext : Context
 {
-    // Static, not AsyncLocal: a lazy-creating AsyncLocal getter poisons the first
-    // reading branch with a fresh empty instance, hiding the framework's later
-    // Current = ... assignment from that branch.
-    private static GlobalContext? _current;
+    // Process-level default instance used by source-gen module initializers that run
+    // before any test session starts (and thus before any AsyncLocal value is set).
+    private static readonly GlobalContext DefaultInstance = new();
+
+    // AsyncLocal so concurrent sessions each get their own context without races.
+    private static readonly AsyncLocal<GlobalContext?> Contexts = new();
+
     public static new GlobalContext Current
     {
-        // Factory overload — the parameterless one uses Activator.CreateInstance<T>(),
-        // which AOT trimming may not preserve for GlobalContext's internal ctor.
-        get => LazyInitializer.EnsureInitialized(ref _current, static () => new GlobalContext())!;
-        internal set => Volatile.Write(ref _current, value);
+        get => Contexts.Value ?? DefaultInstance;
+        internal set => Contexts.Value = value;
     }
 
     internal GlobalContext() : base(null)

TUnit.Engine/TUnitInitializer.cs

@@ -10,6 +10,9 @@ namespace TUnit.Engine;
 
 internal class TUnitInitializer(ICommandLineOptions commandLineOptions, IHookRegistrar hookDiscoveryService)
 {
+    private static volatile bool _globalHandlersConfigured;
+    private static volatile bool _traceListenersConfigured;
+
     public void Initialize(ExecuteRequestContext context)
     {
         ConfigureGlobalExceptionHandlers(context);
@@ -27,6 +30,12 @@ public void Initialize(ExecuteRequestContext context)
 
     private void SetUpExceptionListeners()
     {
+        if (_traceListenersConfigured)
+        {
+            return;
+        }
+
+        _traceListenersConfigured = true;
         Trace.Listeners.Insert(0, new ThrowListener());
     }
 
@@ -50,6 +59,13 @@ private void ParseParameters()
 
     private static void ConfigureGlobalExceptionHandlers(ExecuteRequestContext context)
     {
+        if (_globalHandlersConfigured)
+        {
+            return;
+        }
+
+        _globalHandlersConfigured = true;
+
         // Handle unhandled exceptions on any thread
         AppDomain.CurrentDomain.UnhandledException += (_, args) =>
         {

TUnit.RpcTests/Tests.cs

@@ -79,4 +79,82 @@ public async Task RunTests_WithSkippedTest_ReportsSkippedState(string framework,
 
         await Assert.That(skipped).Count().IsGreaterThan(0);
     }
+
+    [Test]
+    [Timeout(300_000)]
+    [Retry(3)]
+    [MethodDataSource(nameof(Frameworks))]
+    public async Task RunTests_MultipleSequentialSessions_ProducesConsistentResults(string framework, CancellationToken cancellationToken)
+    {
+        await using var session = await TestHostSession.StartAsync(framework, cancellationToken);
+
+        var discovered = await session.DiscoverAsync(cancellationToken);
+
+        var basicTests = discovered
+            .Select(x => x.Node)
+            .Where(node => node.Uid.Contains(".BasicTests."))
+            .ToArray();
+
+        await Assert.That(basicTests).Count().IsGreaterThan(0);
+
+        // Run the same tests 3 times sequentially against the same server process.
+        // Each run should produce the same number of results — verifying that shared
+        // static state (Sources, GlobalContext, hooks) is not drained or corrupted.
+        for (var i = 0; i < 3; i++)
+        {
+            var runUpdates = await session.RunAsync(basicTests, cancellationToken);
+
+            var executed = runUpdates.Where(x => x.Node.ExecutionState is not null and not "in-progress").ToArray();
+            var passed = executed.Count(x => x.Node.ExecutionState == "passed");
+
+            using (Assert.Multiple())
+            {
+                await Assert.That(executed).Count().IsEqualTo(basicTests.Length)
+                    .Because($"Sequential run {i + 1} of 3 should execute all {basicTests.Length} tests");
+                await Assert.That(passed).IsEqualTo(basicTests.Length)
+                    .Because($"Sequential run {i + 1} of 3 should pass all tests");
+            }
+        }
+    }
+
+    [Test]
+    [Timeout(300_000)]
+    [Retry(3)]
+    [MethodDataSource(nameof(Frameworks))]
+    public async Task RunTests_ConcurrentSessions_ProducesResults(string framework, CancellationToken cancellationToken)
+    {
+        await using var session = await TestHostSession.StartAsync(framework, cancellationToken);
+
+        var discovered = await session.DiscoverAsync(cancellationToken);
+
+        var basicTests = discovered
+            .Select(x => x.Node)
+            .Where(node => node.Uid.Contains(".BasicTests."))
+            .ToArray();
+
+        await Assert.That(basicTests).Count().IsGreaterThan(0);
+
+        // Fire 3 concurrent runTests RPCs to the same server process.
+        // With the serialization fix, all should complete with correct results
+        // (they queue up and execute sequentially under the lock).
+        var tasks = Enumerable.Range(0, 3)
+            .Select(_ => session.RunAsync(basicTests, cancellationToken))
+            .ToArray();
+
+        var results = await Task.WhenAll(tasks);
+
+        for (var i = 0; i < results.Length; i++)
+        {
+            var executed = results[i].Where(x => x.Node.ExecutionState is not null and not "in-progress").ToArray();
+            var passed = executed.Count(x => x.Node.ExecutionState == "passed");
+
+            using (Assert.Multiple())
+            {
+                await Assert.That(executed).Count().IsEqualTo(basicTests.Length)
+                    .Because($"Concurrent run {i + 1} of 3 should execute all {basicTests.Length} tests");
+                await Assert.That(passed).IsEqualTo(basicTests.Length)
+                    .Because($"Concurrent run {i + 1} of 3 should pass all tests");
+            }
+        }
+    }
 }