feat: implement instance creation with required property handling

TUnit.Core.SourceGenerator/CodeGenerators/Helpers/InstanceFactoryGenerator.cs

@@ -6,6 +6,37 @@ namespace TUnit.Core.SourceGenerator.CodeGenerators.Helpers;
 
 public static class InstanceFactoryGenerator
 {
+    /// <summary>
+    /// Generates code to create an instance of a type with proper required property handling.
+    /// This handles required properties that don't have data sources by initializing them with defaults.
+    /// </summary>
+    public static void GenerateInstanceCreation(CodeWriter writer, ITypeSymbol typeSymbol, string variableName)
+    {
+        var className = typeSymbol.GloballyQualified();
+        // Use GetAllRequiredProperties because even properties with data sources need to be
+        // initialized in the object initializer to satisfy C#'s required modifier constraint.
+        // The actual values will be populated by the data sources at runtime.
+        var requiredProperties = RequiredPropertyHelper.GetAllRequiredProperties(typeSymbol).ToArray();
+
+        if (requiredProperties.Length == 0)
+        {
+            writer.AppendLine($"{variableName} = new {className}();");
+        }
+        else
+        {
+            writer.AppendLine($"{variableName} = new {className}()");
+            writer.AppendLine("{");
+            writer.Indent();
+            foreach (var property in requiredProperties)
+            {
+                var defaultValue = RequiredPropertyHelper.GetDefaultValueForType(property.Type);
+                writer.AppendLine($"{property.Name} = {defaultValue},");
+            }
+            writer.Unindent();
+            writer.AppendLine("};");
+        }
+    }
+
     public static void GenerateInstanceFactory(CodeWriter writer, ITypeSymbol typeSymbol)
     {
         GenerateInstanceFactory(writer, typeSymbol, null);

TUnit.Core.SourceGenerator/Generators/TestMetadataGenerator.cs

@@ -1048,7 +1048,7 @@ private static void GenerateMethodDataSourceFactory(CodeWriter writer, IMethodSy
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{methodCall};");
@@ -1080,7 +1080,7 @@ private static void GenerateMethodDataSourceFactory(CodeWriter writer, IMethodSy
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{methodCall};");
@@ -1124,7 +1124,7 @@ private static void GenerateMethodDataSourceFactory(CodeWriter writer, IMethodSy
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{methodCall};");
@@ -1167,7 +1167,7 @@ private static void GenerateMethodDataSourceFactory(CodeWriter writer, IMethodSy
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{methodCall};");
@@ -1217,7 +1217,7 @@ private static void GeneratePropertyDataSourceFactory(CodeWriter writer, IProper
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{propertyAccess};");
@@ -1249,7 +1249,7 @@ private static void GeneratePropertyDataSourceFactory(CodeWriter writer, IProper
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{propertyAccess};");
@@ -1293,7 +1293,7 @@ private static void GeneratePropertyDataSourceFactory(CodeWriter writer, IProper
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{propertyAccess};");
@@ -1336,7 +1336,7 @@ private static void GeneratePropertyDataSourceFactory(CodeWriter writer, IProper
                 writer.AppendLine("else");
                 writer.AppendLine("{");
                 writer.Indent();
-                writer.AppendLine($"instance = new {fullyQualifiedType}();");
+                InstanceFactoryGenerator.GenerateInstanceCreation(writer, targetType, "instance");
                 writer.Unindent();
                 writer.AppendLine("}");
                 writer.AppendLine($"var result = (({fullyQualifiedType})instance).{propertyAccess};");

TUnit.TestProject/Bugs/3951/Tests.cs

@@ -0,0 +1,48 @@
+using TUnit.Core.Interfaces;
+using TUnit.TestProject.Attributes;
+
+namespace TUnit.TestProject.Bugs._3951;
+
+
+public sealed class MyTestGeneratorAttribute<T> : DataSourceGeneratorAttribute<T> where T : MyType, new()
+{
+    protected override IEnumerable<Func<T>> GenerateDataSources(DataGeneratorMetadata dataGeneratorMetadata) => [() => new T()];
+}
+
+public class MyType;
+
+public class ErrContext: IAsyncInitializer, IAsyncDisposable
+{
+    public ValueTask DisposeAsync() => default;
+    public Task InitializeAsync() => Task.CompletedTask;
+}
+
+public class ErrFixture<T> : IAsyncDisposable, IAsyncInitializer
+{
+    public required ErrContext Fixture { get; set; }
+    public ValueTask DisposeAsync() => default;
+    public Task InitializeAsync() => Task.CompletedTask;
+}
+
+public class ErrTest
+{
+    [ClassDataSource<ErrFixture<MyType>>(Shared = SharedType.PerClass)]
+    public required ErrFixture<MyType> Fixture { get; init; }
+
+    public IEnumerable<Func<ErrContext>> TestExecutions => [() => Fixture.Fixture];
+
+    [MethodDataSource("TestExecutions")]
+
+    [Test]
+    public async Task MyTest(ErrContext context)
+    {
+        await Assert.That(context.GetType()).IsNotAssignableTo<MyType>();
+    }
+
+    [MyTestGeneratorAttribute<MyType>]
+    [Test]
+    public async Task MyTest2(MyType t)
+    {
+        await Assert.That(t.GetType()).IsAssignableTo<MyType>();
+    }
+}