TestableController.cs

[TestFixture]
public class ControllerTests
{
	[Test]
	public void Foo()
	{
		CustomersController controller = new CustomersController().Testable()
			.WithSession(Session)
			.Authenticated(user => user.Foo = "bar");
		
		controller.Request.Cookies.Add(new HttpCookie("foo"));
	}
}

public static class TestableController
{
	public static T Testable<T>(this T controller) where T : Controller
	{
		var cookies = new HttpCookieCollection();
		
		var request = new Mock<HttpRequestBase>();
		request.Setup(x => x.Cookies).Returns(() => cookies);
		//setup headers and other fluff

		var context = new Mock<HttpContextBase>();
		context.SetupGet(x => x.Request).Returns(request.Object);

		controller.ControllerContext = new ControllerContext(context.Object, new RouteData(), controller);

		return controller;
	}
	
	public static T Authenticated<T>(this T controller, Action<User> setUserProperties) where T : RavenController
	{
		var user = new User();
		setUserProperties(user);

		controller.RavenSession.Store(user);
		controller.RavenSession.SaveChanges();

		var authTicket = new FormsAuthenticationTicket(user.Id.ToString(), false, 1);
		var httpCookie = new HttpCookie(FormsAuthentication.FormsCookieName, FormsAuthentication.Encrypt(authTicket));
		controller.Request.Cookies.Add(httpCookie);

		return controller;
	}

	public static T WithSession<T>(this T controller, IDocumentSession session) where T : RavenController
	{
		controller.RavenSession = session;
		return controller;
	}
}