Unit Test Scanf in c/c++

(Sorry for my english) I'm trying to make a unit test from a code of c++. In the next function (menu) there aren't any parameter into (). But into this funciton there are a scanf,that i would like testing but I haven't any idea how to make it.

Can I test scanf from Unit Test?

Thank you.

Code from function:

void principal::menu()
{
    int choice;
    system("cls");
    printf("\n--------MENU--------");
    printf("\n1 : Jugador X");
    printf("\n2 : Jugador O");
    printf("\n3 : Sortir");
    printf("\nTria el tipus de jugador: ");
    scanf_s("%d", &choice);
    turn = 1;
    switch (choice)
    {
    case 1:
        player = 1;
        comp = 0;
        player_first();
        break;
    case 2:
        player = 0;
        comp = 1;
        start_game();
        break;
    case 3:
        exit(1);
    default:
        menu();
    }
}

Code from test:

...
TEST_METHOD(menu){
   principal p; //this is the class --> not matter now

   //test code
}

If the code have a parameter I use the next code:

 ...
 TEST_METHOD(menu){
   principal p; //this is the class --> not matter now

   //test code
   Assert::AreEqual(result, parameter to enter);
}