test: add regression tests for ClassDataSource with SharedType.None

TUnit.Engine/Building/TestBuilder.cs

@@ -206,7 +206,8 @@ public async Task<IEnumerable<AbstractExecutableTest>> BuildTestsFromMetadataAsy
                     hasAnyClassData = true;
                     classDataLoopIndex++;
 
-                    var classData = DataUnwrapper.Unwrap(await classDataFactory() ?? []);
+                    var classDataResult = await classDataFactory() ?? [];
+                    var classData = DataUnwrapper.Unwrap(classDataResult);
 
                     var needsInstanceForMethodDataSources = metadata.DataSources.Any(ds => ds is IAccessesInstanceData);
 

TUnit.TestProject/ClassDataSourceSharedNoneRegressionTests.cs

@@ -0,0 +1,156 @@
+using TUnit.Core.Interfaces;
+using TUnit.TestProject.Attributes;
+
+namespace TUnit.TestProject;
+
+/// <summary>
+/// Regression tests for GitHub Issue #3855
+/// Verifies that ClassDataSource with SharedType.None constructs and initializes objects only once per test.
+/// </summary>
+[EngineTest(ExpectedResult.Pass)]
+public class ClassDataSourceSharedNoneRegressionTests
+{
+    // Test helper class that tracks construction
+    public class ConstructionCounterClass
+    {
+        private static int _instanceCounter = 0;
+        public int InstanceNumber { get; }
+
+        public ConstructionCounterClass()
+        {
+            InstanceNumber = Interlocked.Increment(ref _instanceCounter);
+        }
+
+        public int Value { get; set; } = 42;
+    }
+
+    // Test helper class that tracks initialization
+    public class AsyncInitializerCounterClass : IAsyncInitializer
+    {
+        private static int _initCounter = 0;
+        public int InitNumber { get; private set; } = -1;
+
+        public Task InitializeAsync()
+        {
+            InitNumber = Interlocked.Increment(ref _initCounter);
+            return Task.CompletedTask;
+        }
+
+        public int Value { get; set; } = 99;
+    }
+
+    /// <summary>
+    /// Test that SharedType.None constructs the class data source exactly once per test.
+    /// Regression test for issue #3855 where it was being constructed twice.
+    /// Before the fix, InstanceNumber would be 2 (constructed twice).
+    /// After the fix, InstanceNumber should be 1 (constructed once).
+    /// </summary>
+    [Test]
+    [ClassDataSource<ConstructionCounterClass>(Shared = SharedType.None)]
+    public async Task SharedTypeNone_ConstructsOnlyOnce(ConstructionCounterClass instance)
+    {
+        // Instance should be constructed exactly once, so InstanceNumber should be 1
+        // (not 2, which would indicate double construction)
+        await Assert.That(instance).IsNotNull();
+        await Assert.That(instance.InstanceNumber).IsEqualTo(1);
+        await Assert.That(instance.Value).IsEqualTo(42);
+    }
+
+    /// <summary>
+    /// Test that SharedType.None with IAsyncInitializer initializes exactly once per test.
+    /// Regression test for issue #3855 where InitializeAsync was being called twice.
+    /// Before the fix, InitNumber would be 2 (initialized twice).
+    /// After the fix, InitNumber should be 1 (initialized once).
+    /// </summary>
+    [Test]
+    [ClassDataSource<AsyncInitializerCounterClass>(Shared = SharedType.None)]
+    public async Task SharedTypeNone_WithAsyncInitializer_InitializesOnlyOnce(AsyncInitializerCounterClass instance)
+    {
+        // Instance should be initialized exactly once, so InitNumber should be 1
+        // (not 2, which would indicate double initialization)
+        await Assert.That(instance).IsNotNull();
+        await Assert.That(instance.InitNumber).IsEqualTo(1);
+        await Assert.That(instance.Value).IsEqualTo(99);
+    }
+}
+
+/// <summary>
+/// Regression tests for GitHub Issue #3855 - Verify no instance leakage across tests.
+/// Tests that multiple test methods in the same class each receive their own unique instance
+/// with SharedType.None (no sharing or leakage across tests).
+/// </summary>
+public class ClassDataSourceSharedNoneNoLeakageTests
+{
+    // Test helper class that tracks instance IDs and mutation
+    public class UniqueInstanceClass
+    {
+        private static int _nextId = 0;
+        public int InstanceId { get; }
+        public int MutationValue { get; set; }
+
+        public UniqueInstanceClass()
+        {
+            InstanceId = Interlocked.Increment(ref _nextId);
+            MutationValue = 0; // Initial value
+        }
+
+        public static void ResetIdCounter()
+        {
+            _nextId = 0;
+        }
+    }
+
+    [Before(TestSession)]
+    public static void ResetCounters()
+    {
+        UniqueInstanceClass.ResetIdCounter();
+    }
+
+    /// <summary>
+    /// First test - should get instance ID 1, mutate it, and not affect other tests
+    /// </summary>
+    [Test]
+    [ClassDataSource<UniqueInstanceClass>(Shared = SharedType.None)]
+    public async Task Test1_GetsUniqueInstance(UniqueInstanceClass instance)
+    {
+        // This is the first test, should have InstanceId = 1
+        await Assert.That(instance.InstanceId).IsEqualTo(1);
+        await Assert.That(instance.MutationValue).IsEqualTo(0);
+
+        // Mutate the instance
+        instance.MutationValue = 100;
+    }
+
+    /// <summary>
+    /// Second test - should get instance ID 2, with fresh MutationValue = 0
+    /// (proves no leakage from Test1)
+    /// </summary>
+    [Test]
+    [ClassDataSource<UniqueInstanceClass>(Shared = SharedType.None)]
+    public async Task Test2_GetsUniqueInstance(UniqueInstanceClass instance)
+    {
+        // This is the second test, should have InstanceId = 2
+        await Assert.That(instance.InstanceId).IsEqualTo(2);
+
+        // MutationValue should be 0 (not affected by Test1's mutation to 100)
+        await Assert.That(instance.MutationValue).IsEqualTo(0);
+
+        // Mutate the instance
+        instance.MutationValue = 200;
+    }
+
+    /// <summary>
+    /// Third test - should get instance ID 3, with fresh MutationValue = 0
+    /// (proves no leakage from Test1 or Test2)
+    /// </summary>
+    [Test]
+    [ClassDataSource<UniqueInstanceClass>(Shared = SharedType.None)]
+    public async Task Test3_GetsUniqueInstance(UniqueInstanceClass instance)
+    {
+        // This is the third test, should have InstanceId = 3
+        await Assert.That(instance.InstanceId).IsEqualTo(3);
+
+        // MutationValue should be 0 (not affected by Test1 or Test2)
+        await Assert.That(instance.MutationValue).IsEqualTo(0);
+    }
+}