ASP.NET MVC test for action filters

This blog post from Scott Hanselmann covers MvcMockHelpers including FakeHttpContext for different mocking frameworks among others also Moq:

using System;
using System.Web;
using System.Text.RegularExpressions;
using System.IO;
using System.Collections.Specialized;
using System.Web.Mvc;
using System.Web.Routing;
using Moq;

namespace UnitTests
{
    public static class MvcMockHelpers
    {
        public static HttpContextBase FakeHttpContext()
        {
            var context = new Mock<httpcontextbase>();
            var request = new Mock<httprequestbase>();
            var response = new Mock<httpresponsebase>();
            var session = new Mock<httpsessionstatebase>();
            var server = new Mock<httpserverutilitybase>();

            context.Expect(ctx => ctx.Request).Returns(request.Object);
            context.Expect(ctx => ctx.Response).Returns(response.Object);
            context.Expect(ctx => ctx.Session).Returns(session.Object);
            context.Expect(ctx => ctx.Server).Returns(server.Object);

            return context.Object;
        }

        public static HttpContextBase FakeHttpContext(string url)
        {
            HttpContextBase context = FakeHttpContext();
            context.Request.SetupRequestUrl(url);
            return context;
        }

        public static void SetFakeControllerContext(this Controller controller)
        {
            var httpContext = FakeHttpContext();
            ControllerContext context = new ControllerContext(new RequestContext(httpContext, new RouteData()), controller);
            controller.ControllerContext = context;
        }

        static string GetUrlFileName(string url)
        {
            if (url.Contains("?"))
                return url.Substring(0, url.IndexOf("?"));
            else
                return url;
        }

        static NameValueCollection GetQueryStringParameters(string url)
        {
            if (url.Contains("?"))
            {
                NameValueCollection parameters = new NameValueCollection();

                string[] parts = url.Split("?".ToCharArray());
                string[] keys = parts[1].Split("&".ToCharArray());

                foreach (string key in keys)
                {
                    string[] part = key.Split("=".ToCharArray());
                    parameters.Add(part[0], part[1]);
                }

                return parameters;
            }
            else
            {
                return null;
            }
        }

        public static void SetHttpMethodResult(this HttpRequestBase request, string httpMethod)
        {
            Mock.Get(request)
                .Expect(req => req.HttpMethod)
                .Returns(httpMethod);
        }

        public static void SetupRequestUrl(this HttpRequestBase request, string url)
        {
            if (url == null)
                throw new ArgumentNullException("url");

            if (!url.StartsWith("~/"))
                throw new ArgumentException("Sorry, we expect a virtual url starting with \"~/\".");

            var mock = Mock.Get(request);

            mock.Expect(req => req.QueryString)
                .Returns(GetQueryStringParameters(url));
            mock.Expect(req => req.AppRelativeCurrentExecutionFilePath)
                .Returns(GetUrlFileName(url));
            mock.Expect(req => req.PathInfo)
                .Returns(string.Empty);
        }
    }
}

Another good resource for ASP.NET MVC test helpers is the MvcContrib project on CodePlex.

After you have a FakeHttpContext you can test your action filter:

var context = new ActionExecutedContext();
context.HttpContext = MvcMockHelpers.FakeHttpContext();
context.Result = new EmpytResult(); // or whatever the default result should be

var filter = new MyCustomAttribute();
filter.OnActionExecuted(context);

Assert.True(context.Result is EmpytResult);
...