在 Web 中进行测试驱动的开发，比较大的困难是模拟 HttpContext;
1.Nop提供了完整的FakeHttpContext实现，如图
1.FakeHttpContext的作用。
控制器进行单元测试时模拟web上下文环境，还有一些其他对HttpContext有依赖的组件也可以使用Fake从而进行组件的单元测试。
2.例举Nop中使用到FakeHttpContext的地方
(1).NopEngine(初始化NopEngine时，是web环境就注册真实HttpContext，否则注册FakeHttpContext)
//HTTP context and other related stuff
builder.Register(c =>
//register FakeHttpContext when HttpContext is not available
HttpContext.Current != null ?
(new HttpContextWrapper(HttpContext.Current) as HttpContextBase) :
(new FakeHttpContext("~/") as HttpContextBase))
.As<HttpContextBase>()
.InstancePerHttpRequest();
builder.Register(c => c.Resolve<HttpContextBase>().Request)
.As<HttpRequestBase>()
.InstancePerHttpRequest();
builder.Register(c => c.Resolve<HttpContextBase>().Response)
.As<HttpResponseBase>()
.InstancePerHttpRequest();
builder.Register(c => c.Resolve<HttpContextBase>().Server)
.As<HttpServerUtilityBase>()
.InstancePerHttpRequest();
builder.Register(c => c.Resolve<HttpContextBase>().Session)
.As<HttpSessionStateBase>()
.InstancePerHttpRequest();
(2)RoutesTests( Route依赖HttpContextBase，可以用Fake类代替 )
[Test]
public void Blog_routes()
{
//TODO why does it pass null instead of "new BlogPagingFilteringModel()" as it's done in real application? The same is about issue is in the other route test methods
"~/blog/".ShouldMapTo<BlogController>(c => c.List(null));
"~/blog/rss/1".ShouldMapTo<BlogController>(c => c.ListRss(1));
"~/blog/2/".ShouldMapTo<BlogController>(c => c.BlogPost(2));
"~/blog/2/test-se-name".ShouldMapTo<BlogController>(c => c.BlogPost(2));
//TODO validate properties such as 'Tag' or 'Month' in the passed BlogPagingFilteringModel. The same is about issue is in the other route test methods
//"~/blog/tag/sometag".ShouldMapTo<BlogController>(c => c.List(new BlogPagingFilteringModel() { Tag = "sometag" }));
//"~/blog/month/3".ShouldMapTo<BlogController>(c => c.List(new BlogPagingFilteringModel() { Month = "4" }));
}
(3)其他组件，如WebHelperTests，AdminAuthorizeAttributeTests都依赖了HttpContextBase
总结：这些Fake类为单元测试提供了模拟的Web上下文环境。，再也不用担心控制器以及类库因为用了HttpContextBase（最常见的包括Session，Request，Response）而变得难以进行单元测试了（但在控制器中还是应该尽量少用这些）