Prevent sealed class mocks

.gitignore

@@ -1,5 +1,6 @@
 
 /.vs
+*.idea/
 
 bin/
 obj/

Moq.AutoMock.Tests/DescribeCreateInstance.cs

@@ -1,7 +1,5 @@
-using System;
-using Microsoft.VisualStudio.TestTools.UnitTesting;
+
 using Moq.AutoMock.Resolvers;
-using Moq.AutoMock.Tests.Util;
 
 namespace Moq.AutoMock.Tests;
 
@@ -218,6 +216,16 @@ public void It_includes_reason_why_nested_constructor_was_rejected()
         Assert.AreEqual("Rejecting constructor Moq.AutoMock.Tests.DescribeCreateInstance+HasMultipleConstructors(Moq.AutoMock.Tests.DescribeCreateInstance+HasStringParameter hasString), because AutoMocker was unable to create parameter 'Moq.AutoMock.Tests.DescribeCreateInstance+HasStringParameter hasString'", ex.DiagnosticMessages[1]);
     }
 
+    [TestMethod]
+    public void It_can_create_instances_of_nested_sealed_classes()
+    {
+        AutoMocker mocker = new();
+        mocker.Resolvers.Add(new InstanceResolver());
+        var mockWithSealedService = mocker.CreateInstance<HasNestedSealedService>();
+
+        Assert.AreEqual(mockWithSealedService.SealedService, mockWithSealedService.NestedSealedService.SealedService);
+    }
+
     private class CustomStringResolver : IMockResolver
     {
         public CustomStringResolver(string stringValue)
@@ -267,6 +275,18 @@ public HasMultipleConstructorsNested(HasStringParameter hasString)
         }
     }
 
+    public class HasNestedSealedService
+    {
+        public SealedService SealedService { get; set; }
+        public WithSealedService NestedSealedService { get; set; }
+
+        public HasNestedSealedService(SealedService sealedService, WithSealedService nestedSealedService)
+        {
+            SealedService = sealedService;
+            NestedSealedService = nestedSealedService;
+        }
+    }
+
     public record class ConcreteDependency(IService1 Service);
     public record class ConcreteDependencyIsFirst(ConcreteDependency Dependency, IService1 Service);
     public record class ConcreteDependencyIsSecond(IService1 Service, ConcreteDependency Dependency);

Moq.AutoMock.Tests/DescribeGetMock.cs

@@ -82,4 +82,12 @@ public void It_returns_null_for_unmockable_object_via_iserviceprovider()
         var service = mocker.GetService(typeof(string));
         Assert.IsNull(service);
     }
+
+    [TestMethod]
+    public void It_throws_when_mocking_a_sealed_class()
+    {
+        var mocker = new AutoMocker();
+        var act = () => mocker.GetMock<SealedService>();
+        Assert.ThrowsException<ArgumentException>(act);
+    }
 }

Moq.AutoMock.Tests/Util/SealedService.cs

@@ -0,0 +1,9 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace Moq.AutoMock.Tests.Util;
+
+[ExcludeFromCodeCoverage]
+public sealed class SealedService
+{
+    public SealedService() { }
+}

Moq.AutoMock.Tests/Util/WithSealedService.cs

@@ -0,0 +1,14 @@
+using System.Diagnostics.CodeAnalysis;
+
+namespace Moq.AutoMock.Tests.Util;
+
+[ExcludeFromCodeCoverage]
+public class WithSealedService
+{
+    public SealedService SealedService { get; set; }
+
+    public WithSealedService(SealedService service)
+    {
+        SealedService = service;
+    }
+}

Moq.AutoMock/AutoMocker.cs

@@ -3,6 +3,7 @@
 using System.Reflection;
 using System.Runtime.ExceptionServices;
 using System.Text;
+using Moq.AutoMock.Extensions;
 using Moq.AutoMock.Resolvers;
 using Moq.Language;
 using Moq.Language.Flow;
@@ -78,7 +79,7 @@ public AutoMocker(MockBehavior mockBehavior, DefaultValue defaultValue, DefaultV
             new LazyResolver(),
             new FuncResolver(),
             new CancellationTokenResolver(),
-            new MockResolver(mockBehavior, defaultValue, defaultValueProvider, callBase),
+            new MockResolver(mockBehavior, defaultValue, defaultValueProvider, callBase)
         };
     }
 
@@ -219,6 +220,12 @@ public object CreateInstance(Type type, bool enablePrivate)
         if (type is null) throw new ArgumentNullException(nameof(type));
 
         var context = new ObjectGraphContext(enablePrivate);
+
+        return CreateInstanceInternal(type, context);
+    }
+
+    internal object CreateInstanceInternal(Type type, ObjectGraphContext context)
+    {
         if (!TryGetConstructorInvocation(type, context, out ConstructorInfo? ctor, out IInstance[]? arguments))
         {
             throw new ObjectCreationException(
@@ -987,6 +994,10 @@ public void Verify<T, TResult>(Expression<Func<T, TResult>> expression, Times ti
 
     internal Mock? CreateMock(Type serviceType, MockBehavior mockBehavior, DefaultValue defaultValue, DefaultValueProvider? defaultValueProvider, bool callBase, ObjectGraphContext objectGraphContext)
     {
+        if (!serviceType.IsMockable())
+        {
+            return null;
+        }
         var mockType = typeof(Mock<>).MakeGenericType(serviceType);
 
         bool mayHaveDependencies = serviceType.IsClass

Moq.AutoMock/Resolvers/InstanceResolver.cs

@@ -0,0 +1,19 @@
+namespace Moq.AutoMock.Resolvers;
+
+/// <summary>
+/// A resolver that resolves requested types with a created instance.
+/// </summary>
+public class InstanceResolver : IMockResolver
+{
+    /// <summary>
+    /// Resolves requested types with created instances.
+    /// </summary>
+    /// <param name="context">The resolution context.</param>
+    public void Resolve(MockResolutionContext context)
+    {
+        if (context.AutoMocker.CreateInstanceInternal(context.RequestType, context.ObjectGraphContext) is { } instance)
+        {
+            context.Value = instance;
+        }
+    }
+}