Add tests validating @dynamicModel decorator behavior

Co-authored-by: m-nash <[email protected]>

Author: Copilot

packages/http-client-csharp/generator/Microsoft.TypeSpec.Generator/test/DynamicModelSerializationTests.cs

@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System.Collections.Generic;
+using System.Reflection;
+using Microsoft.TypeSpec.Generator.Input;
+using Microsoft.TypeSpec.Generator.Primitives;
+using Microsoft.TypeSpec.Generator.Providers;
+using Microsoft.TypeSpec.Generator.Tests.Common;
+using NUnit.Framework;
+
+namespace Microsoft.TypeSpec.Generator.Tests.Providers
+{
+    public class DynamicModelSerializationTests
+    {
+        [SetUp]
+        public void Setup()
+        {
+            MockHelpers.LoadMockGenerator();
+        }
+        [Test]
+        public void DynamicModelSerialization()
+        {
+            var properties = new[]
+            {
+                InputFactory.Property("id", InputPrimitiveType.String, isRequired: true),
+                InputFactory.Property("name", InputPrimitiveType.String, isRequired: true),
+                InputFactory.Property("email", InputPrimitiveType.String, isRequired: false)
+            };
+
+            // Create a model with the dynamicModel decorator
+            var inputModel = InputFactory.Model("User", properties: properties);
+            
+            // Use reflection to set decorators since the property has an internal setter
+            var decoratorsProperty = typeof(InputType).GetProperty("Decorators");
+            var decorators = new List<InputDecoratorInfo>
+            {
+                new InputDecoratorInfo("dynamicModel", null)
+            };
+            decoratorsProperty?.SetValue(inputModel, decorators);
+
+            var modelProvider = new ModelProvider(inputModel);
+            var writer = new TypeProviderWriter(modelProvider);
+            var file = writer.Write();
+
+            // Verify the model doesn't have the raw data field
+            Assert.That(file.Content, Does.Not.Contain("_additionalBinaryDataProperties"));
+            
+            // Verify the model has the Patch property
+            Assert.That(file.Content, Contains.Substring("public object Patch { get; set; }"));
+        }
+
+        [Test]
+        public void RegularModelStillHasRawDataField()
+        {
+            var properties = new[]
+            {
+                InputFactory.Property("id", InputPrimitiveType.String, isRequired: true),
+                InputFactory.Property("name", InputPrimitiveType.String, isRequired: true)
+            };
+
+            // Create a regular model without the dynamicModel decorator
+            var inputModel = InputFactory.Model("RegularUser", properties: properties);
+
+            var modelProvider = new ModelProvider(inputModel);
+            var writer = new TypeProviderWriter(modelProvider);
+            var file = writer.Write();
+
+            // Verify the model has the raw data field
+            Assert.That(file.Content, Contains.Substring("_additionalBinaryDataProperties"));
+            
+            // Verify the model doesn't have the Patch property
+            Assert.That(file.Content, Does.Not.Contain("public object Patch { get; set; }"));
+        }
+    }
+}