void Ex03()
 {
     Given("a controller to which the IUserAuthentication is not specified", () =>
     {
         Controller = new LoginContentController(Navigator, null);
         AvaloniaController.SetDataContext(LoginContent, Controller);
     });
     When("to click the login button", () =>
          AvaloniaController.EventHandlersOf(Controller)
          .GetBy("LoginButton")
          .Raise(nameof(Button.Click))
          );
     Then("the content should not be navigated to any contents", () =>
     {
         Navigator.DidNotReceive().NavigateTo(Arg.Any <object>());
     });
     Then("the LoginNotAvailable message should be set", () => LoginContent.Message.Value == Resources.LoginNotAvailable);
 }
        public LoginContentControllerSpec()
        {
            Controller = new LoginContentController(Navigator, UserAuthentication);

            AvaloniaController.SetDataContext(LoginContent, Controller);
        }