单元测试HtmlHelper扩展方法失败

Question

我正在尝试测试HtmlHelper我编写的一些扩展方法.我的第一个问题是如何创建一个HtmlHelper实例,但我使用这个代码解决了这个问题:

private static HtmlHelper<T> CreateHtmlHelper<T>(T model)
{
    var viewDataDictionary = new ViewDataDictionary(model);
    var controllerContext = new ControllerContext(new Mock<HttpContextBase>().Object,
    new RouteData(),
    new Mock<ControllerBase>().Object);

    var viewContext = new ViewContext(controllerContext, new Mock<IView>().Object, viewDataDictionary, new TempDataDictionary(), new Mock<TextWriter>().Object);

    var mockViewDataContainer = new Mock<IViewDataContainer>();
mockViewDataContainer.Setup(v => v.ViewData).Returns(viewDataDictionary);

    return new HtmlHelper<T>(viewContext, mockViewDataContainer.Object);
}

我的几个测试现在工作正常,但有一个测试会引发异常.测试定义如下:

// Arrange
var inputDictionary = CreateDictionary();
var htmlHelper = CreateHtmlHelper(inputDictionary);

// Act
var actualHtmlString = htmlHelper.EditorFor(m => m.Dict, model).ToHtmlString();
...

该EditorFor方法是我的扩展方法.在该方法的某处,进行以下调用:

tagBuilder.MergeAttributes(htmlHelper.GetUnobtrusiveValidationAttributes(expression, metadata));    

从我的单元测试执行此代码时,抛出以下异常:

System.NullReferenceExceptionObject reference not set to an instance of an object.
   at System.Web.Mvc.ViewContext.ScopeCache.Get(IDictionary`2 scope, HttpContextBase httpContext)
   at System.Web.Mvc.ViewContext.get_UnobtrusiveJavaScriptEnabled()
   at System.Web.Mvc.HtmlHelper.GetUnobtrusiveValidationAttributes(String name, ModelMetadata metadata)
   at AspNetMvcDictionarySerialization.HtmlHelperExtensions.InputTagHelper(HtmlHelper htmlHelper, ModelMetadata metadata, InputType inputType, String expression, IDictionary`2 htmlAttributes, String fullName, Int32 index, String fieldType, String val) in HtmlHelperExtensions.cs: line 154

所以代码失败了ScopeCache.Get,但为什么呢？有谁知道如何解决这个问题？

Answer 1

我最终做的是查看ASP.NET MVC的源代码.在他们的代码中,他们也测试HtmlHelper实例.他们使用名为的实用程序类来实现MvcHelper,它提供HtmlHelper了使用正确准备的HTTP上下文创建新实例的便捷方法.

删除我不需要的代码后,我最终得到了以下类:

public static class MvcHelper
{
    public static HtmlHelper<TModel> GetHtmlHelper<TModel>(TModel inputDictionary)
    {
        var viewData = new ViewDataDictionary<TModel>(inputDictionary);
        var mockViewContext = new Mock<ViewContext> { CallBase = true };
        mockViewContext.Setup(c => c.ViewData).Returns(viewData);
        mockViewContext.Setup(c => c.HttpContext.Items).Returns(new Hashtable());

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

    public static IViewDataContainer GetViewDataContainer(ViewDataDictionary viewData)
    {
        var mockContainer = new Mock<IViewDataContainer>();
        mockContainer.Setup(c => c.ViewData).Returns(viewData);
        return mockContainer.Object;
    }
}

使用此帮助程序类,我的代码正确执行.

我已经为完整的帮助程序类创建了一个要点,以便于包含在您的项目中:https://gist.github.com/ErikSchierboom/6da474dcd5751fbbc94c