Updating ActionContext for the default constructor and the setter methods

src/Microsoft.AspNet.Mvc.Core/ActionContext.cs

@@ -12,6 +12,17 @@ namespace Microsoft.AspNet.Mvc
     /// </summary>
     public class ActionContext
     {
+        /// <summary>
+        /// Creates a empty <see cref="ActionContext"/>.
+        /// </summary>
+        /// <remarks>
+        /// The default constructor is provided for unit test purposes only.
+        /// </remarks>
+        public ActionContext()
+        {
+            ModelState = new ModelStateDictionary();
+        }
+
         /// <summary>
         /// Creates a new <see cref="ActionContext"/>.
         /// </summary>
@@ -56,23 +67,44 @@ namespace Microsoft.AspNet.Mvc
         }
 
         /// <summary>
-        /// Gets the <see cref="Mvc.ActionDescriptor"/> for the selected action.
+        /// Gets or sets the <see cref="Mvc.ActionDescriptor"/> for the selected action.
         /// </summary>
-        public ActionDescriptor ActionDescriptor { get; }
+        /// <remarks>
+        /// The property setter is provided for unit test purposes only.
+        /// </remarks>
+        public ActionDescriptor ActionDescriptor
+        {
+            get; set;
+        }
 
         /// <summary>
-        /// Gets the <see cref="Http.HttpContext"/> for the current request.
+        /// Gets or sets the <see cref="Http.HttpContext"/> for the current request.
         /// </summary>
-        public HttpContext HttpContext { get; }
+        /// <remarks>
+        /// The property setter is provided for unit test purposes only.
+        /// </remarks>
+        public HttpContext HttpContext
+        {
+            get; set;
+        }
 
         /// <summary>
         /// Gets the <see cref="ModelStateDictionary"/>.
         /// </summary>
-        public ModelStateDictionary ModelState { get; }
+        public ModelStateDictionary ModelState
+        {
+            get;
+        }
 
         /// <summary>
-        /// Gets the <see cref="AspNet.Routing.RouteData"/> for the current request.
+        /// Gets or sets the <see cref="AspNet.Routing.RouteData"/> for the current request.
         /// </summary>
-        public RouteData RouteData { get; }
+        /// <remarks>
+        /// The property setter is provided for unit test purposes only.
+        /// </remarks>
+        public RouteData RouteData
+        {
+            get; set;
+        }
     }
 }

src/Microsoft.AspNet.Mvc.Core/Controller.cs

@@ -20,6 +20,7 @@ namespace Microsoft.AspNet.Mvc
     {
         private DynamicViewData _viewBag;
         private ViewDataDictionary _viewData;
+        private ActionContext _actionContext;
 
         public IServiceProvider Resolver
         {
@@ -69,8 +70,32 @@ namespace Microsoft.AspNet.Mvc
             }
         }
 
+        /// <summary>
+        /// Gets or sets the <see cref="Mvc.ActionContext"/> object.
+        /// </summary>
+        /// <remarks>
+        /// <see cref="IControllerActivator"/> activates this property while activating controllers. If user codes
+        /// directly instantiate controllers, the getter returns an empty <see cref="Mvc.ActionContext"/>.
+        /// </remarks>
         [Activate]
-        public ActionContext ActionContext { get; set; }
+        public ActionContext ActionContext
+        {
+            get
+            {
+                // This should run only for the controller unit test scenarios
+                _actionContext = _actionContext ?? new ActionContext();
+                return _actionContext;
+            }
+            set
+            {
+                if (value == null)
+                {
+                    throw new ArgumentNullException(nameof(value));
+                }
+
+                _actionContext = value;
+            }
+        }
 
         [Activate]
         public ActionBindingContext BindingContext { get; set; }

test/Microsoft.AspNet.Mvc.Core.Test/ControllerUnitTestabilityTests.cs

@@ -5,7 +5,11 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
+using Microsoft.AspNet.Http;
+using Microsoft.AspNet.Mvc.ModelBinding;
+using Microsoft.AspNet.Routing;
 using Microsoft.AspNet.WebUtilities;
+using Moq;
 using Xunit;
 
 namespace Microsoft.AspNet.Mvc
@@ -424,6 +428,83 @@ namespace Microsoft.AspNet.Mvc
             Assert.Throws<ArgumentException>(() => controller.Redirect_Action(null));
         }
 
+        [Fact]
+        public void ControllerActionContext_ReturnsNotNull()
+        {
+            // Arrange && Act
+            var controller = new TestabilityController();
+
+            // Assert
+            Assert.NotNull(controller.ActionContext);
+            Assert.NotNull(controller.ActionContext.ModelState);
+            Assert.Null(controller.ActionContext.ActionDescriptor);
+            Assert.Null(controller.ActionContext.HttpContext);
+            Assert.Null(controller.ActionContext.RouteData);
+        }
+
+        [Fact]
+        public void ActionContextDefaultConstructor_CanBeUsedForControllerActionContext()
+        {
+            // Arrange
+            var actionContext = new ActionContext();
+            var controller = new TestabilityController();
+
+            // Act
+            controller.ActionContext = actionContext;
+
+            // Assert
+            Assert.Equal(actionContext.HttpContext, controller.Context);
+            Assert.Equal(actionContext.RouteData, controller.RouteData);
+            Assert.Equal(actionContext.ModelState, controller.ModelState);
+        }
+
+        [Fact]
+        public void ActionContextSetters_CanBeUsedWithControllerActionContext()
+        {
+            // Arrange
+            var actionDescriptor = new Mock<ActionDescriptor>();
+            var httpContext = new Mock<HttpContext>();
+            var routeData = new Mock<RouteData>();
+
+            var actionContext = new ActionContext()
+            {
+                ActionDescriptor = actionDescriptor.Object,
+                HttpContext = httpContext.Object,
+                RouteData = routeData.Object,
+            };
+
+            var controller = new TestabilityController();
+
+            // Act
+            controller.ActionContext = actionContext;
+
+            // Assert
+            Assert.Equal(httpContext.Object, controller.Context);
+            Assert.Equal(routeData.Object, controller.RouteData);
+            Assert.Equal(actionContext.ModelState, controller.ModelState);
+            Assert.Equal(actionDescriptor.Object, actionContext.ActionDescriptor);
+        }
+
+        [Fact]
+        public void ActionContextModelState_ShouldBeSameAsViewDataAndControllerModelState()
+        {
+            // Arrange
+            var actionContext = new ActionContext();
+            var controller1 = new Controller();
+            var controller2 = new Controller();
+
+            // Act
+            controller2.ActionContext = actionContext;
+
+            // Assert
+            Assert.Equal(controller1.ModelState, controller1.ActionContext.ModelState);
+            Assert.Equal(controller1.ModelState, controller1.ViewData.ModelState);
+
+            Assert.Equal(actionContext.ModelState, controller2.ModelState);
+            Assert.Equal(actionContext.ModelState, controller2.ActionContext.ModelState);
+            Assert.Equal(actionContext.ModelState, controller2.ViewData.ModelState);
+        }
+
         public static IEnumerable<object[]> TestabilityViewTestData
         {
             get