Render a View during a Unit Test - ControllerContext.DisplayMode

Question

I am working on an ASP.NET MVC 4 web application that generates large and complicated reports. I want to write Unit Tests that render a View in order to make sure the View doesn't blow up depending on the Model:

 [Test]
 public void ExampleTest(){                  
     var reportModel = new ReportModel();

     var reportHtml = RenderRazorView(
           @"..\..\Report.Mvc\Views\Report\Index.cshtml", 
           reportModel);

     Assert.IsFalse(
         string.IsNullOrEmpty(reportHtml),
         "View Failed to Render!");          
 }

 public string RenderRazorView(string viewPath, object model){
    //WHAT GOES HERE?
 }

I have seen a lot of information about this around the web, but it's either arguing against testing vies, or can only be used in the context of a web request.

• Arguing Against - Unit Testing the Views? - This concludes there should be no logic in the View so you should only need to test compilation. I think there is value in testing the View to make sure there aren't Null Reference Exceptions, the correct sections are shown, etc.
• Context of a Web Request - Render a view as a string - This is to render a View to be sent in an email. But this approach requires being called via a web request (ie a valid HttpContextBase).

I have been working to adapt Render a view as a string to work with a Mocked HttpContextBase, but have been running into problems when using a Mocked ControllerContext:

Object reference not set to an instance of an object. at System.Web.WebPages.DisplayModeProvider.GetDisplayMode(HttpContextBase context) at System.Web.Mvc.ControllerContext.get_DisplayMode() at System.Web.Mvc.VirtualPathProviderViewEngine.GetPath(ControllerContext controllerContext, String[] locations, String[] areaLocations, String locationsPropertyName, String name, String controllerName, String cacheKeyPrefix, Boolean useCache, String[]& searchedLocations)

This is the code I have so far:

    public string RenderRazorView(string viewPath, object model)
    {
        var controller = GetMockedDummyController();

        //Exception here
        var viewResult = 
            ViewEngines.Engines.FindView(controller.ControllerContext, "Index", "");

        using (var sw = new StringWriter())
        {
            var viewContext =
                new ViewContext(
                    controller.ControllerContext,
                    viewResult.View,
                    new ViewDataDictionary(model),
                    new TempDataDictionary(),
                    sw);

            viewResult.View.Render(viewContext, sw);

            return sw.ToString();
        }
    }

I'm building the Controller:

    private Controller GetMockedDummyController()
    {
        var HttpContextBaseMock = new Mock<HttpContextBase>();
        var HttpRequestMock = new Mock<HttpRequestBase>();
        var HttpResponseMock = new Mock<HttpResponseBase>();
        HttpContextBaseMock.SetupGet(x => x.Request).Returns(HttpRequestMock.Object);
        HttpContextBaseMock.SetupGet(x => x.Response).Returns(HttpResponseMock.Object);

        var controller = new DummyController();

        var routeData = new RouteData();
        routeData.Values.Add("controller", "Dummy");

        controller.ControllerContext = 
            new ControllerContext(
                HttpContextBaseMock.Object,
                routeData,
                controller);

        controller.Url =
            new UrlHelper(
                new RequestContext(
                    HttpContextBaseMock.Object,
                    routeData), 
                new RouteCollection());

        return controller;
    }

The DummyController is just public class DummyController : Controller {}

Question

Give the path to a View, how can I render it to HTML from a Test project? Or more specifically, how can I mock out the ControllerContext.DisplayMode?

Answer 1

Assuming you have complete separation of concerns, is it necessary to instantiate the controller at all? If not, then perhaps you can use RazorEngine to test your views.

var contents = File.ReadAllText("pathToView"); 
var result = Razor.Parse(contents,model);
// assert here

Answer 2

You will need an empty Controller just for testing (ex TestController)

public class WebMvcHelpers
{
    public static string GetViewPageHtml(object model, string viewName)
    {
        System.Web.Mvc.Controller controller = CreateController<TestController>();

        ViewEngineResult result = ViewEngines.Engines.FindPartialView(controller.ControllerContext, viewName);

        if (result.View == null)
            throw new Exception(string.Format("View Page {0} was not found", viewName));

        controller.ViewData.Model = model;
        StringBuilder sb = new StringBuilder();
        using (StringWriter sw = new StringWriter(sb))
        {
            using (System.Web.UI.HtmlTextWriter output = new System.Web.UI.HtmlTextWriter(sw))
            {
                ViewContext viewContext = new ViewContext(controller.ControllerContext, result.View, controller.ViewData, controller.TempData, output);
                result.View.Render(viewContext, output);
            }
        }

        return sb.ToString();
    }

    /// <summary>
    /// Creates an instance of an MVC controller from scratch 
    /// when no existing ControllerContext is present       
    /// </summary>
    /// <typeparam name="T">Type of the controller to create</typeparam>
    /// <returns></returns>
    public static T CreateController<T>(RouteData routeData = null)
                where T : System.Web.Mvc.Controller, new()
    {
        T controller = new T();

        // Create an MVC Controller Context
        HttpContextBase wrapper = null;
        if (HttpContext.Current != null)
            wrapper = new HttpContextWrapper(System.Web.HttpContext.Current);
        //else
        //    wrapper = CreateHttpContextBase(writer);


        if (routeData == null)
            routeData = new RouteData();

        if (!routeData.Values.ContainsKey("controller") && !routeData.Values.ContainsKey("Controller"))
            routeData.Values.Add("controller", controller.GetType().Name
                                                        .ToLower()
                                                        .Replace("controller", ""));

        controller.ControllerContext = new System.Web.Mvc.ControllerContext(wrapper, routeData, controller);
        return controller;
    }
}

public class TestController : Controller
{
    public ActionResult Index()
    {
        return View();
    }
}