WebSecurity.Login(model.Username, model.Password, model.RememberMe)

public ActionResult Login(LoginModel model, string returnUrl)
{
  if (ModelState.IsValid && !string.IsNullOrEmpty(model.Username) && !string.IsNullOrEmpty(model.Password))
            {
                if (WebSecurity.UserExists(model.Username))
                {
                    if (WebSecurity.IsConfirmed(model.Username))
                    {
                        if (WebSecurity.Login(model.Username, model.Password, model.RememberMe)) // **Exception is thrown at this line**
                        {
                            return RedirectUser(model);
                        }
                    }
                }
            }
}

[TestMethod]
    public void T01_Case106()
    {
        var ac_controller = DependencyResolver.Current.GetService<AccountController>();
        var login_response = ac_controller.Login(_testStudio.LoginModel, string.Empty);
        Assert.IsNotNull(login_response);

    }


  public class TestStudio
    {
        public LoginModel LoginModel = new LoginModel { Username = "admin@gr.com", Password = "1234567"
    };

System.NullReferenceException: Object reference not set to an instance of an object.
at System.Web.Security.FormsAuthentication.SetAuthCookie(String userName, Boolean createPersistentCookie, String strCookiePath)
at System.Web.Security.FormsAuthentication.SetAuthCookie(String userName, Boolean createPersistentCookie)
at WebMatrix.WebData.WebSecurity.Login(String userName, String password, Boolean persistCookie)
at Groove.Controllers.Web.AccountController.Login(LoginModel model, String returnUrl) in D:projectGrooveWebGrooveControllersWebAccountController.cs:line 89