Mocking ViewContext to test validation error messages

Question

Here's the story. In order to be able to drop well-formed Bootstrap controls into my MVC forms, I'm building an HtmlHelper extension method that generates the following structure with a single command:

<div class="control-group">
    @Html.LabelFor(m => m.UserName, new { @class = "control-label" })
    <div class="controls">
        <div class="input-prepend">
            <span class="add-on"><i class="icon-user"></i></span>
            @Html.TextBoxFor(m => m.UserName, new { @class = "input-xlarge" })
        </div>
        @Html.ValidationMessageFor(m => m.UserName)
    </div>
</div>

The method itself isn't that hard to write. What is considerably more difficult is the unit testing. To make my extension method testable, I need to create an instance of HtmlHelper<T> using the appropriate mocks. To that end, I have tweaked the answer to an old StackOverflow question and come up with this:

public static HtmlHelper<TModel> CreateHtmlHelper<TModel>(bool clientValidationEnabled, bool unobtrusiveJavascriptEnabled, ViewDataDictionary dictionary = null)
{
    if (dictionary == null)
        dictionary = new ViewDataDictionary { TemplateInfo = new TemplateInfo() };

    var mockViewContext = new Mock<ViewContext>(
        new ControllerContext(
            new Mock<HttpContextBase>().Object,
            new RouteData(),
            new Mock<ControllerBase>().Object),
        new Mock<IView>().Object,
        dictionary,
        new TempDataDictionary(),
        new Mock<TextWriter>().Object);

    mockViewContext.SetupGet(c => c.UnobtrusiveJavaScriptEnabled).Returns(unobtrusiveJavascriptEnabled);
    mockViewContext.SetupGet(c => c.FormContext).Returns(new FormContext { FormId = "myForm" });
    mockViewContext.SetupGet(c => c.ClientValidationEnabled).Returns(clientValidationEnabled);
    mockViewContext.SetupGet(c => c.ViewData).Returns(dictionary);
    var mockViewDataContainer = new Mock<IViewDataContainer>();
    mockViewDataContainer.Setup(v => v.ViewData).Returns(dictionary);

    return new HtmlHelper<TModel>(mockViewContext.Object, mockViewDataContainer.Object);
}

So far so good. Now that I can create an HtmlHelper object, I can execute my test as follows:

// ARRANGE
ModelMetadataProviders.Current = new DataAnnotationsModelMetadataProvider();
var helper = MvcMocks.CreateHtmlHelper<TestModel>(true, true);
helper.ViewData.Model = new TestModel { Field = null };
helper.ViewData.ModelState.AddModelError("Field", "The field must be assigned.");

// ACT
var controlGroup = helper.ControlGroupFor(m => m.Field, CssClasses.IconUser).ToHtmlString();

Here is the problem. Within ControlGroupFor, whose signature is

    public static HtmlString ControlGroupFor<TModel, TValue>(this HtmlHelper<TModel> html, Expression<Func<TModel, TValue>> expression, string iconClass)

and which I haven't completed yet (being a good little TDD developer), I'm invoking var validationMessage = html.ValidationMessageFor(expression). Despite my use of AddModelError, the ValidationMessageFor method seems to think that html.ViewData.ModelState["Field"] is either null or its ModelErrors collection is empty. I am inferring this because the value of validationMessage is

<span class="field-validation-valid" data-valmsg-for="Field" data-valmsg-replace="true"></span>

and according to Resharper, the ValidationMessageFor method calls down into this method:

    private static MvcHtmlString ValidationMessageHelper(this HtmlHelper htmlHelper, ModelMetadata modelMetadata, string expression, string validationMessage, IDictionary<string, object> htmlAttributes)
    {
        string modelName = htmlHelper.ViewContext.ViewData.TemplateInfo.GetFullHtmlFieldName(expression);
        FormContext formContext = htmlHelper.ViewContext.GetFormContextForClientValidation();

        if (!htmlHelper.ViewData.ModelState.ContainsKey(modelName) && formContext == null)
        {
            return null;
        }

        ModelState modelState = htmlHelper.ViewData.ModelState[modelName];
        ModelErrorCollection modelErrors = (modelState == null) ? null : modelState.Errors;
        ModelError modelError = (((modelErrors == null) || (modelErrors.Count == 0)) ? null : modelErrors.FirstOrDefault(m => !String.IsNullOrEmpty(m.ErrorMessage)) ?? modelErrors[0]);

        if (modelError == null && formContext == null)
        {
            return null;
        }

        TagBuilder builder = new TagBuilder("span");
        builder.MergeAttributes(htmlAttributes);
        builder.AddCssClass((modelError != null) ? HtmlHelper.ValidationMessageCssClassName : HtmlHelper.ValidationMessageValidCssClassName);

        if (!String.IsNullOrEmpty(validationMessage))
        {
            builder.SetInnerText(validationMessage);
        }
        else if (modelError != null)
        {
            builder.SetInnerText(GetUserErrorMessageOrDefault(htmlHelper.ViewContext.HttpContext, modelError, modelState));
        }

        if (formContext != null)
        {
            bool replaceValidationMessageContents = String.IsNullOrEmpty(validationMessage);

            if (htmlHelper.ViewContext.UnobtrusiveJavaScriptEnabled)
            {
                builder.MergeAttribute("data-valmsg-for", modelName);
                builder.MergeAttribute("data-valmsg-replace", replaceValidationMessageContents.ToString().ToLowerInvariant());
            }
            else
            {
                FieldValidationMetadata fieldMetadata = ApplyFieldValidationMetadata(htmlHelper, modelMetadata, modelName);
                // rules will already have been written to the metadata object
                fieldMetadata.ReplaceValidationMessageContents = replaceValidationMessageContents; // only replace contents if no explicit message was specified

                // client validation always requires an ID
                builder.GenerateId(modelName + "_validationMessage");
                fieldMetadata.ValidationMessageId = builder.Attributes["id"];
            }
        }

        return builder.ToMvcHtmlString(TagRenderMode.Normal);
    }

Now, according to everything I've done, the validationMessage should give me a span with a class of field-validation-error and an error message reading "The field must be assigned." In my watch window, html.ViewData.ModelState["Field"].Errors has a count of 1. I must be missing something. Can anyone see what it is?

Answer 1

I modified the test to use ViewContext.ViewData rather than ViewData directly:

// ARRANGE
ModelMetadataProviders.Current = new DataAnnotationsModelMetadataProvider();
var helper = MvcMocks.CreateHtmlHelper<TestModel>(true, true);
helper.ViewContext.ViewData.Model = new TestModel { Field = null };
helper.ViewContext.ViewData.ModelState.AddModelError("Field", "The field must be assigned.");

// ACT
var controlGroup = helper.ControlGroupFor(m => m.Field, CssClasses.IconUser).ToHtmlString();

This has fixed my issue, but it's still not clear to me why helper.ViewContext.ViewData and helper.ViewData should be pointing to different instances, given the way the mocks were set up.