I've seen people testing that RenderView is called by a controller by inheriting into a "testable" controller. Madness!

RenderView is just a convenience method that calls to IViewEngine, so why not just test expectations on that with a mock? We basically want to test that the correct ViewContext is sent to the RenderView method of the view engine.

This is my test:

[TestFixture]
public class HomeControllerTests : ControllerTestsBase<HomeController>
{
    public override HomeController CreateController()
    {
        return new HomeController();
    }

    [Test]
    public void Renders_Index()
    {
        var render = ExpectRenderView();

        Controller.Index();

        Assert.That(render.Data.ViewName, Is.EqualTo("Index"));
    }
}

I don't think we can get more straight forward than that!

This is my test base class:
(I'm using Moq as the mock framework.)

public abstract class ControllerTestsBase<T>
    where T : Controller
{
    public T Controller;
    public Mock<IViewEngine> ViewEngine;

    [SetUp]
    public virtual void SetUp()
    {
        Controller = CreateController();
        ViewEngine = new Mock<IViewEngine>();
        Controller.ViewEngine = ViewEngine.Object;

        Controller.ControllerContext = new Mock<ControllerContext>(new Mock<HttpContextBase>().Object, new RouteData(), Controller).Object;
    }

    public abstract T CreateController();

    public RenderCall<ViewContext> ExpectRenderView()
    {
        var render = new RenderCall<ViewContext>();
        ViewEngine.Expect(v => v.RenderView(It.IsAny<ViewContext>()))
            .Callback(new Action<ViewContext>(render.Set));
        return render;
    }
}

The RenderCall class provides a place to receive the view context that is passed.

public class RenderCall<T>
{
    bool _called;
    T _data;

    public T Data
    {
        get
        {
            if (!_called) throw new InvalidOperationException("View was not rendered.");
            return _data;
        }
    }

    public void Set(T data)
    {
        _data = data;
        _called = true;
    }
}