ASP.NET MVC: Unit testing session variables does't change - asp.net-mvc

Question

I'm trying to unit test a Logout action of my controller. My controller recive an interface wich deals with session variables:
public HomeController(IUnitOfWork unitOfWork, ISecurityService security = null)
{
_unitOfWork = unitOfWork;
if (security != null)
{
_securityService = security;
}
else
{
_userService = new UserService(_unitOfWork)
_securityService = new SecurityService(_userService);
}
}
Using Moq, I create a HttpSessionStateBase object
Which I use to create a SecurityService object in my unit test class:
var mockSession = new Mock<HttpSessionStateBase>();
mockSession.SetupGet(s => s["UserID"]).Returns("1");
HttpSessionStateBase session = mockSession.Object;
ISecurityService _securityService = new SecurityService(_userService, session);
My SecurityService
public class SecurityService : ISecurityService
{
private readonly IUsuarioService _userService ;
private readonly HttpSessionStateBase _session;
public int UserID
{
get { return Convert.ToInt32(_session["UserID"]); }
set { _session["UserID"] = value; }
}
public SecurityService(IUserService service, HttpSessionStateBase session = null)
{
_userService = service;
_session = session ?? new HttpSessionStateWrapper(HttpContext.Current.Session);
}
public void Logout()
{
// I'm trying to delete this variable, but I can't
_session["UserID"] = 0;
_session.Clear();
_session.Abandon();
}
}
Finally, my test method
[TestMethod]
public void Should_delete_session_variable_from_the_user()
{
controller.Logout();
// It's allways 1
Assert.IsTrue(Convert.ToInt32(session["UserID"]) == 0);
}
When I debug this code, I can see that the session variable does not chage its value. But, if I open a "Quick Watch" window and execute _session["UserID"] = 0;, its value change.
I can't understand why. This is the first time that I see that a variable does not chage its value in debugging.

Answer 1

Finally I found, the solution is to add an SetupSet method.
This is the final code:
int sessionValue = 0;
var mockSession = new Mock<HttpSessionStateBase>();
mockSession.SetupSet(s => s["UserId"] = It.IsAny<int>())
.Callback((string name, object val) => sessionValue = (int) val);
mockSession.SetupGet(s => s["UserId"]).Returns(() => sessionValue);