单元测试的HtmlHelper扩展方法失败 [英] Unit testing HtmlHelper extension method fails

问题描述

我想测试我已经写了一些的HtmlHelper 扩展方法。我的第一个问题是如何创建一个的HtmlHelper 实例，但我解决了使用这种code：

I am trying to test some HtmlHelper extension methods I have written. My first problem was how to create a HtmlHelper instance, but I solved that using this code:

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，现在工作得很好，但有一个测试抛出异常。测试定义如下：

Several of my tests now work fine, but there is one test that throws an exception. The test is defined as follows:

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

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

的 EditorFor 方法是我的扩展方法。某处在该方法中，以下调用时：

The EditorFor method is my extension method. Somewhere in that method, the following call is made:

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

这是，当这个code是从我的单元测试执行下列异常被抛出：

It is that when this code is executed from my unit test that the following exception is thrown:

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，code在 ScopeCache.Get 失败了，但是为什么呢？没有人有任何想法如何解决这个问题？

So the code fails in ScopeCache.Get, but why? Does anyone have any idea how to solve this?

推荐答案

我最终什么了做一直在寻找在源ASP.NET MVC 的code。在他们的code，他们还测试的HtmlHelper 实例。他们这样做是使用 MvcHelper 命名的一个工具类，它提供了方便的方法来用正确的$ P创建新的的HtmlHelper 实例$ ppared HTTP上下文。

What I ended up doing was looking at the source code of ASP.NET MVC. In their code, they also test HtmlHelper instances. They do so using a utility class named MvcHelper, which provides convenience methods to create new HtmlHelper instance with a correctly prepared HTTP context.

删除code，我并不需要后，我结束了以下类：

After removing the code I did not need, I ended up with the following class:

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;
    }
}

有了这个辅助类，我的code正确执行。

With this helper class, my code executed correctly.

我已经建立了完整的辅助类一个依据，以便容易纳入项目：<一href=\"https://gist.github.com/ErikSchierboom/6da474dcd5751fbbc94c\">https://gist.github.com/ErikSchierboom/6da474dcd5751fbbc94c

I have created a gist for the complete helper class to allow for easy inclusion in your project: https://gist.github.com/ErikSchierboom/6da474dcd5751fbbc94c

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