diff --git a/TUnit.Mocks.SourceGenerator.Tests/MockGeneratorTests.cs b/TUnit.Mocks.SourceGenerator.Tests/MockGeneratorTests.cs
index ad61c62f9c..23eafab4d0 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/MockGeneratorTests.cs
+++ b/TUnit.Mocks.SourceGenerator.Tests/MockGeneratorTests.cs
@@ -1347,6 +1347,33 @@ void M()
         return VerifyGeneratorOutput(source);
     }
 
+    [Test]
+    public Task Class_With_Required_Members()
+    {
+        // Regression for #5678: when a partial-mocked base class has `required` members,
+        // the generated impl ctor must carry [SetsRequiredMembers] so the factory can
+        // `new XxxMockImpl(engine)` without CS9035 (member must be initialized).
+        var source = """
+            using TUnit.Mocks;
+
+            public class ConfigBase
+            {
+                public required string Name { get; set; }
+                public required object Settings { get; init; }
+            }
+
+            public class TestUsage
+            {
+                void M()
+                {
+                    var mock = Mock.Of<ConfigBase>();
+                }
+            }
+            """;
+
+        return VerifyGeneratorOutput(source);
+    }
+
     [Test]
     public Task SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf()
     {
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Constructor_Parameters_Extension_Discovery.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Constructor_Parameters_Extension_Discovery.verified.txt
index 08d9c6c884..9219227ce4 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Constructor_Parameters_Extension_Discovery.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Constructor_Parameters_Extension_Discovery.verified.txt
@@ -10,14 +10,17 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine) : base()
         {
             _engine = engine;
         }
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine, string connectionString, int timeout) : base(connectionString, timeout)
         {
             _engine = engine;
         }
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine, string connectionString, int timeout, bool verbose) : base(connectionString, timeout, verbose)
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Required_Members.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Required_Members.verified.txt
new file mode 100644
index 0000000000..31065db736
--- /dev/null
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Required_Members.verified.txt
@@ -0,0 +1,84 @@
+// <auto-generated/>
+#nullable enable
+
+namespace TUnit.Mocks.Generated
+{
+    file sealed class ConfigBaseMockImpl : global::ConfigBase, global::TUnit.Mocks.IRaisable, global::TUnit.Mocks.IMockObject
+    {
+        private readonly global::TUnit.Mocks.MockEngine<global::ConfigBase> _engine;
+
+        [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+        global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
+
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
+        internal ConfigBaseMockImpl(global::TUnit.Mocks.MockEngine<global::ConfigBase> engine) : base()
+        {
+            _engine = engine;
+        }
+
+        [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
+        public void RaiseEvent(string eventName, object? args)
+        {
+            throw new global::System.InvalidOperationException($"No event named '{eventName}' exists on this mock.");
+        }
+    }
+
+    file static class ConfigBasePartialMockFactory
+    {
+        [global::System.Runtime.CompilerServices.ModuleInitializer]
+        internal static void Register()
+        {
+            global::TUnit.Mocks.MockRegistry.RegisterFactory<global::ConfigBase>(Create);
+        }
+
+        private static global::TUnit.Mocks.Mock<global::ConfigBase> Create(global::TUnit.Mocks.MockBehavior behavior, object[] constructorArgs)
+        {
+            var engine = new global::TUnit.Mocks.MockEngine<global::ConfigBase>(behavior);
+            var impl = new ConfigBaseMockImpl(engine);
+            engine.Raisable = impl;
+            var mock = new global::TUnit.Mocks.Mock<global::ConfigBase>(impl, engine);
+            return mock;
+        }
+    }
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#nullable enable
+
+namespace TUnit.Mocks.Generated
+{
+    public static class ConfigBase_MockMemberExtensions
+    {
+    }
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#nullable enable
+
+namespace TUnit.Mocks
+{
+    public static class ConfigBase_MockStaticExtension
+    {
+        extension(global::ConfigBase _)
+        {
+            public static global::TUnit.Mocks.Mock<global::ConfigBase> Mock(global::TUnit.Mocks.MockBehavior behavior = global::TUnit.Mocks.MockBehavior.Loose)
+            {
+                return global::TUnit.Mocks.Mock.Of<global::ConfigBase>(behavior);
+            }
+        }
+    }
+}
+
+
+// ===== FILE SEPARATOR =====
+
+// <auto-generated/>
+#nullable enable
+
+namespace TUnit.Mocks.Generated;
\ No newline at end of file
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Same_Arity_Constructor_Overloads.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Same_Arity_Constructor_Overloads.verified.txt
index c0852b973a..3a2564e389 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Same_Arity_Constructor_Overloads.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Class_With_Same_Arity_Constructor_Overloads.verified.txt
@@ -10,18 +10,22 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine, string name) : base(name)
         {
             _engine = engine;
         }
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine, int id) : base(id)
         {
             _engine = engine;
         }
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine, string host, int port) : base(host, port)
         {
             _engine = engine;
         }
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine, int timeout, bool verbose) : base(timeout, verbose)
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/GenerateMock_Attribute_With_Concrete_Class.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/GenerateMock_Attribute_With_Concrete_Class.verified.txt
index 70eee77d19..3439ef3b15 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/GenerateMock_Attribute_With_Concrete_Class.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/GenerateMock_Attribute_With_Concrete_Class.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal MyServiceMockImpl(global::TUnit.Mocks.MockEngine<global::MyService> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt
index 1afb836cfc..75c955cf57 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Interface_With_Obsolete_Members.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal BaseDialogMockImpl(global::TUnit.Mocks.MockEngine<global::BaseDialog> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
index faad323967..fb3c5eb9c1 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated.ExternalLib
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal ExternalClientMockImpl(global::TUnit.Mocks.MockEngine<global::ExternalLib.ExternalClient> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt
index 51eef9d8cd..58be91736b 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Filters_Members_With_Internal_Signature_Types.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated.ExternalLib
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal ServiceClientMockImpl(global::TUnit.Mocks.MockEngine<global::ExternalLib.ServiceClient> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Omits_Inaccessible_Property_Setters.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Omits_Inaccessible_Property_Setters.verified.txt
index 2f1debed02..fceed0883d 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Omits_Inaccessible_Property_Setters.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_Omits_Inaccessible_Property_Setters.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated.ExternalLib
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal ExternalResponseMockImpl(global::TUnit.Mocks.MockEngine<global::ExternalLib.ExternalResponse> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
index a9fa6b6db0..1894f961d5 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Partial_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal BaseServiceMockImpl(global::TUnit.Mocks.MockEngine<global::BaseService> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt
index 72e6bbdcba..64fd05b306 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/SelfEquatable_Generates_EqualsOf_GetHashCodeOf_ToStringOf.verified.txt
@@ -10,6 +10,7 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal SelfEquatableSnapshotMockImpl(global::TUnit.Mocks.MockEngine<global::SelfEquatableSnapshot> engine) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
index b8485e4f70..b81b6b45f7 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_Filters_Internal_Virtual_Members_From_External_Assembly.verified.txt
@@ -11,6 +11,7 @@ namespace TUnit.Mocks.Generated.ExternalLib
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal ExternalServiceWrapMockImpl(global::TUnit.Mocks.MockEngine<global::ExternalLib.ExternalService> engine, global::ExternalLib.ExternalService wrappedInstance) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
index 2edd07f51c..1d5618a378 100644
--- a/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
+++ b/TUnit.Mocks.SourceGenerator.Tests/Snapshots/Wrap_Mock_With_Generic_Constrained_Virtual_Methods.verified.txt
@@ -11,6 +11,7 @@ namespace TUnit.Mocks.Generated
         [global::System.ComponentModel.EditorBrowsable(global::System.ComponentModel.EditorBrowsableState.Never)]
         global::TUnit.Mocks.IMock? global::TUnit.Mocks.IMockObject.MockWrapper { get; set; }
 
+        [global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]
         internal RepositoryWrapMockImpl(global::TUnit.Mocks.MockEngine<global::Repository> engine, global::Repository wrappedInstance) : base()
         {
             _engine = engine;
diff --git a/TUnit.Mocks.SourceGenerator/Builders/MockImplBuilder.cs b/TUnit.Mocks.SourceGenerator/Builders/MockImplBuilder.cs
index 4ecadf46bf..9834275dc6 100644
--- a/TUnit.Mocks.SourceGenerator/Builders/MockImplBuilder.cs
+++ b/TUnit.Mocks.SourceGenerator/Builders/MockImplBuilder.cs
@@ -5,6 +5,9 @@ namespace TUnit.Mocks.SourceGenerator.Builders;
 
 internal static class MockImplBuilder
 {
+    // Suppresses CS9035: ctor claims responsibility for required members so factory can `new XxxMockImpl(engine)` without initializers.
+    private const string SetsRequiredMembersAttribute = "[global::System.Diagnostics.CodeAnalysis.SetsRequiredMembers]";
+
     public static void BuildInto(CodeWriter writer, MockTypeModel model)
     {
         var safeName = GetCompositeShortSafeName(model);
@@ -151,6 +154,7 @@ private static void GenerateWrapConstructors(CodeWriter writer, MockTypeModel mo
 
         if (model.Constructors.Length == 0)
         {
+            writer.AppendLine(SetsRequiredMembersAttribute);
             using (writer.Block($"internal {safeName}WrapMockImpl(global::TUnit.Mocks.MockEngine<{mockableType}> engine, {model.FullyQualifiedName} wrappedInstance)"))
             {
                 writer.AppendLine("_engine = engine;");
@@ -167,6 +171,7 @@ private static void GenerateWrapConstructors(CodeWriter writer, MockTypeModel mo
         {
             if (ctor.Parameters.Length == 0)
             {
+                writer.AppendLine(SetsRequiredMembersAttribute);
                 using (writer.Block($"internal {safeName}WrapMockImpl(global::TUnit.Mocks.MockEngine<{mockableType}> engine, {model.FullyQualifiedName} wrappedInstance) : base()"))
                 {
                     writer.AppendLine("_engine = engine;");
@@ -181,6 +186,7 @@ private static void GenerateWrapConstructors(CodeWriter writer, MockTypeModel mo
             {
                 var paramList = string.Join(", ", ctor.Parameters.Select(p => $"{p.FullyQualifiedType} {p.Name}"));
                 var argList = string.Join(", ", ctor.Parameters.Select(p => p.Name));
+                writer.AppendLine(SetsRequiredMembersAttribute);
                 using (writer.Block($"internal {safeName}WrapMockImpl(global::TUnit.Mocks.MockEngine<{mockableType}> engine, {model.FullyQualifiedName} wrappedInstance, {paramList}) : base({argList})"))
                 {
                     writer.AppendLine("_engine = engine;");
@@ -496,6 +502,7 @@ private static void GeneratePartialConstructors(CodeWriter writer, MockTypeModel
         if (model.Constructors.Length == 0)
         {
             // No explicit constructors found, generate a default one
+            writer.AppendLine(SetsRequiredMembersAttribute);
             using (writer.Block($"internal {safeName}MockImpl(global::TUnit.Mocks.MockEngine<{mockableType}> engine)"))
             {
                 writer.AppendLine("_engine = engine;");
@@ -512,6 +519,7 @@ private static void GeneratePartialConstructors(CodeWriter writer, MockTypeModel
             if (ctor.Parameters.Length == 0)
             {
                 // Parameterless constructor
+                writer.AppendLine(SetsRequiredMembersAttribute);
                 using (writer.Block($"internal {safeName}MockImpl(global::TUnit.Mocks.MockEngine<{mockableType}> engine) : base()"))
                 {
                     writer.AppendLine("_engine = engine;");
@@ -526,6 +534,7 @@ private static void GeneratePartialConstructors(CodeWriter writer, MockTypeModel
                 // Constructor with parameters - pass them through to base
                 var paramList = string.Join(", ", ctor.Parameters.Select(p => $"{p.FullyQualifiedType} {p.Name}"));
                 var argList = string.Join(", ", ctor.Parameters.Select(p => p.Name));
+                writer.AppendLine(SetsRequiredMembersAttribute);
                 using (writer.Block($"internal {safeName}MockImpl(global::TUnit.Mocks.MockEngine<{mockableType}> engine, {paramList}) : base({argList})"))
                 {
                     writer.AppendLine("_engine = engine;");
diff --git a/TUnit.Mocks.Tests/KitchenSinkEdgeCasesTests.cs b/TUnit.Mocks.Tests/KitchenSinkEdgeCasesTests.cs
index 6c80ed6a16..4855fe9530 100644
--- a/TUnit.Mocks.Tests/KitchenSinkEdgeCasesTests.cs
+++ b/TUnit.Mocks.Tests/KitchenSinkEdgeCasesTests.cs
@@ -201,11 +201,22 @@ public interface ICancellableStream
     IAsyncEnumerable<int> Stream(CancellationToken ct = default);
 }
 
-// ─── T17 SKIPPED. `required` members on a mock target produce CS9035
-//     ("required member must be set in the object initializer") in the
-//     generated factory. The factory would need to emit [SetsRequiredMembers]
-//     on its constructor and skip initializing required members. Separate
-//     generator fix.
+// ─── T17. `required` members on a mock target ───────────────────────────────
+
+public abstract class RequiredShape
+{
+    public required string Name { get; init; }
+    public abstract int Compute();
+}
+
+public abstract class RequiredMixed
+{
+    public required string Title { get; init; }
+    public required int Count { get; init; }
+    public required System.Guid Id { get; init; }
+    public abstract string Describe();
+    public virtual int Bonus() => 0;
+}
 
 // ─── T18 SKIPPED. Member names matching C# keywords (`class`, `event`, `record`)
 //     are passed through to the generator as unescaped identifiers, producing
@@ -570,7 +581,39 @@ static async IAsyncEnumerable<int> Yield(params int[] values)
         }
     }
 
-    // T17 test elided — see the SKIPPED note above the type declarations.
+    // ── T17 ──
+
+    [Test]
+    public async Task T17_Required_Property_Does_Not_Block_Mock_Instantiation()
+    {
+        var mock = RequiredShape.Mock();
+        mock.Compute().Returns(123);
+
+        await Assert.That(mock.Object.Compute()).IsEqualTo(123);
+        mock.Compute().WasCalled(Times.Once);
+
+        // Required members intentionally remain at default in mocks; [SetsRequiredMembers] suppresses CS9035 only.
+        await Assert.That(mock.Object.Name).IsNull();
+    }
+
+    [Test]
+    public async Task T17_Multiple_Required_Members_Reference_And_Value_Types()
+    {
+        var mock = RequiredMixed.Mock();
+        mock.Describe().Returns("hello");
+        mock.Bonus().Returns(7);
+
+        await Assert.That(mock.Object.Describe()).IsEqualTo("hello");
+        await Assert.That(mock.Object.Bonus()).IsEqualTo(7);
+
+        mock.Describe().WasCalled(Times.Once);
+        mock.Bonus().WasCalled(Times.Once);
+
+        // Required members intentionally remain at default in mocks; [SetsRequiredMembers] suppresses CS9035 only.
+        await Assert.That(mock.Object.Title).IsNull();
+        await Assert.That(mock.Object.Count).IsEqualTo(0);
+        await Assert.That(mock.Object.Id).IsEqualTo(System.Guid.Empty);
+    }
 
     // T18 test elided — see the SKIPPED note above the type declarations.