How do I write a unit test for controller use automapper?

I'm trying to write a unit test for controller to test method return all users. But I confuse How can I write unit test with automapper

Controller :

private readonly IUserService _userService;

public UserController(IUserService userService)
{
  this._userService = userService;
}

public ActionResult List()
{
  var users = _userService.GetAllUsers().ToList();
  var viewModel = Mapper.Map<List<UserViewModel>>(users);
  return View(viewModel);
}

Controller Test:

    private Mock<IUserService> _userServiceMock;
    UserController objUserController;
    List<UserViewModel> listUser;

    [SetUp]
    public void Initialize()
    {
        _userServiceMock = new Mock<IUserService>();
        objUserController = new UserController(_userServiceMock.Object);
        listUser = new List<UserViewModel>()
        {
            new UserViewModel() {Id = 1, Active = true, Password = "123456", UserName = "hercules"},
            new UserViewModel() {Id = 2, Active = false, Password = "1234567", UserName = "alibaba"},
            new UserViewModel() {Id = 3, Active = true, Password = "12345678", UserName = "robinhood"},
        };
    }

    [Test]
    public void Index_Returns_AllUser()
    {
      // How do I here ???
    }