Difference between HttpContext and HttpContextWrapper in terms of Unit Testing and in terms of Web Forms and MVC

Question

I know the difference between HttpContext and HttpContextWrapper is below...

HttpContext

This is the vintage asp.net c

Answer 1

I heard that it's useful in Unit Testing in comparing with Web Forms. but how it's useful ?

Let's take an example of an ASP.NET MVC controller action which is adding a cookie to the response:

public class HomeController : Controller
{
    public ActionResult Index()
    {
        var cookie = new HttpCookie("foo", "bar");
        this.Response.Cookies.Add(cookie);
        return View();
    }
}

Notice the Response property over there. It's an HttpResponseBase. So we can mock it in a unit test:

public class HttpResponseMock: HttpResponseBase
{
    private HttpCookieCollection cookies;
    public override HttpCookieCollection Cookies
    {
        get
        {
            if (this.cookies == null)
            {
                this.cookies = new HttpCookieCollection();
            }

            return this.cookies;
        }
    }
}

public class HttpContextMock: HttpContextBase
{
    private HttpResponseBase response;

    public override HttpResponseBase Response
    {
        get 
        {
            if (this.response == null)
            {
                this.response = new HttpResponseMock();
            }
            return this.response;
        }
    }
}

and now we could write a unit test:

// arrange
var sut = new HomeController();
var httpContext = new HttpContextMock();
sut.ControllerContext = new ControllerContext(httpContext, new RouteData(), sut);

// act
var actual = sut.Index();

// assert
Assert.AreEqual("bar", sut.Response.Cookies["foo"].Value);

And since all members are virtual we could use a mocking framework which would avoid us the need to write those mock classes for the unit test. For example with NSubstitute here's how the test might look:

// arrange
var sut = new HomeController();
var context = Substitute.For();
var response = Substitute.For();
var cookies = new HttpCookieCollection();
context.Response.Returns(response);
context.Response.Cookies.Returns(cookies);
sut.ControllerContext = new ControllerContext(context, new RouteData(), sut);

// act
var actual = sut.Index();

// assert
Assert.AreEqual("bar", sut.Response.Cookies["foo"].Value);

Now let's take a WebForm:

protected void Page_Load(object sender, EventArgs)
{
    var cookie = new HttpCookie("foo", "bar");
    this.Response.Cookies.Add(cookie);
}

In this case the Response property is the concrete HttpResponse. So you are busted. Impossible to unit test in isolation.