Weird “Object reference not set to an instance of an object” error while using Moq

When you set up Moq, you need to additionally configure your HttpContext, otherwise your Request will be null. You can set it up in a function in your controller that you call at the beginning of your test case, something like:

private Mock<ControllerContext> GetContextBase()
{
    var fakeHttpContext = new Mock<HttpContextBase>();
    var request = new Mock<HttpRequestBase>();
    var response = new Mock<HttpResponseBase>();
    var session = new MockHttpSession();
    var server = new MockServer();
    var parms = new RequestParams();
    var uri = new Uri("http://TestURL/Home/Index");

    var fakeIdentity = new GenericIdentity("DOMAIN\\username");
    var principal = new GenericPrincipal(fakeIdentity, null);

    request.Setup(t => t.Params).Returns(parms);
    request.Setup(t => t.Url).Returns(uri);
    fakeHttpContext.Setup(t => t.User).Returns(principal);
    fakeHttpContext.Setup(ctx => ctx.Request).Returns(request.Object);
    fakeHttpContext.Setup(ctx => ctx.Response).Returns(response.Object);
    fakeHttpContext.Setup(ctx => ctx.Session).Returns(session);
    fakeHttpContext.Setup(ctx => ctx.Server).Returns(server);

    var controllerContext = new Mock<ControllerContext>();
    controllerContext.Setup(t => t.HttpContext).Returns(fakeHttpContext.Object);

    return controllerContext;
}

The supporting classes are along the lines of:

/// <summary>
/// A Class to allow simulation of SessionObject
/// </summary>
public class MockHttpSession : HttpSessionStateBase
{
    Dictionary<string, object> m_SessionStorage = new Dictionary<string, object>();

    public override object this[string name]
    {
        get {
            try
            {
                return m_SessionStorage[name];
            }
            catch (Exception e)
            {
                return null;
            }
        }
        set { m_SessionStorage[name] = value; }
    }

}

public class RequestParams : System.Collections.Specialized.NameValueCollection
{
    Dictionary<string, string> m_SessionStorage = new Dictionary<string, string>();

    public override void Add(string name, string value)
    {
        m_SessionStorage.Add(name, value);
    }

    public override string Get(string name)
    {
        return m_SessionStorage[name];
    }

}

public class MockServer : HttpServerUtilityBase
{
    public override string MapPath(string path)
    {

        return @"C:\YourCodePathTowherever\" + path;
    }
}

Lastly, in the top of your Test method, just add this call:

// Arrange
HomeController controller = new HomeController();
controller.ControllerContext = GetContextBase().Object;

That will give you a Request object to work with :)

[edit]

Name spaces you'll need are:

using System.Security.Principal;
using Microsoft.VisualStudio.TestTools.UnitTesting;
using Moq;