fix: ensure IClassConstructor and ITestEndEventReceiver share the same instance for state management

TUnit.Core/Helpers/ClassConstructorHelper.cs

@@ -50,9 +50,9 @@ public static class ClassConstructorHelper
             return null;
         }
 
-        // Use the ClassConstructor to create the instance
-        var classConstructorType = classConstructorAttribute.ClassConstructorType;
-        var classConstructor = (IClassConstructor)Activator.CreateInstance(classConstructorType)!;
+        // Reuse existing ClassConstructor if already set, otherwise create new instance
+        var classConstructor = testBuilderContext.ClassConstructor
+            ?? (IClassConstructor)Activator.CreateInstance(classConstructorAttribute.ClassConstructorType)!;
 
         testBuilderContext.ClassConstructor = classConstructor;
 

TUnit.Core/TestBuilderContext.cs

@@ -57,7 +57,11 @@ internal static TestBuilderContext FromTestContext(TestContext testContext, IDat
     {
         return new TestBuilderContext
         {
-            Events = testContext.InternalEvents, TestMetadata = testContext.Metadata.TestDetails.MethodMetadata, DataSourceAttribute = dataSourceAttribute, StateBag = testContext.StateBag.Items,
+            Events = testContext.InternalEvents,
+            TestMetadata = testContext.Metadata.TestDetails.MethodMetadata,
+            DataSourceAttribute = dataSourceAttribute,
+            StateBag = testContext.StateBag.Items,
+            ClassConstructor = testContext.ClassConstructor,
         };
     }
 }

TUnit.Engine/Building/TestBuilder.cs

@@ -290,7 +290,8 @@ public async Task<IEnumerable<AbstractExecutableTest>> BuildTestsFromMetadataAsy
                                     Events = new TestContextEvents(),
                                     StateBag = new ConcurrentDictionary<string, object?>(),
                                     DataSourceAttribute = methodDataSource,
-                                    InitializedAttributes = testBuilderContext.InitializedAttributes  // Preserve attributes from parent context
+                                    InitializedAttributes = testBuilderContext.InitializedAttributes,  // Preserve attributes from parent context
+                                    ClassConstructor = testBuilderContext.ClassConstructor  // Preserve ClassConstructor for instance creation
                                 };
 
                                 classData = DataUnwrapper.Unwrap(await classDataFactory() ?? []);

TUnit.TestProject/Bugs/3939/Tests.cs

@@ -0,0 +1,53 @@
+using System.Diagnostics.CodeAnalysis;
+using TUnit.Core.Interfaces;
+using TUnit.TestProject.Attributes;
+
+namespace TUnit.TestProject.Bugs._3939;
+
+/// <summary>
+/// Regression test for issue #3939: IClassConstructor and ITestEndEventReceiver
+/// should use the same instance so that state can be shared (e.g., DI scope disposal).
+/// </summary>
+public sealed class ScopedClassConstructor : IClassConstructor, ITestEndEventReceiver
+{
+    private object? _scope;
+
+    public Task<object> Create([DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type type, ClassConstructorMetadata classConstructorMetadata)
+    {
+        // Simulate creating a DI scope - this should be available in OnTestEnd
+        _scope = new object();
+        return Task.FromResult<object>(new Tests());
+    }
+
+    public ValueTask OnTestEnd(TestContext context)
+    {
+        // This should be called on the SAME instance that Create() was called on
+        // If _scope is null, it means a different instance was used - this is the bug!
+        if (_scope == null)
+        {
+            throw new InvalidOperationException(
+                "Issue #3939: _scope was null in OnTestEnd(), indicating a different IClassConstructor " +
+                "instance was used than the one where Create() was called. " +
+                "IClassConstructor and ITestEndEventReceiver must use the same instance.");
+        }
+
+        // Simulate disposing the scope
+        _scope = null;
+        return default;
+    }
+
+    public int Order => 0;
+}
+
+[EngineTest(ExpectedResult.Pass)]
+[ClassConstructor<ScopedClassConstructor>]
+public sealed class Tests
+{
+    [Test]
+    public Task TestMethod()
+    {
+        // The actual test - just verifies the test runs
+        // The real assertion is in OnTestEnd - it will throw if different instances are used
+        return Task.CompletedTask;
+    }
+}