存储库不会从我的测试方法返回值

我是单元测试的新手，我正在尝试为以下服务方法编写单元测试：

public InventoryViewModel GetInventory(DateTime startDate, DateTime endDate, long roomServiceId)
{
    InventoryViewModel inv = new InventoryViewModel();
    var roomService = _unitOfWork.RoomServiceRepository.GetByID(roomServiceId);
    if (roomService == null)
        throw new InvalidOperationException("there is not the roomService");
        ....
    }
...
}

此方法

工作正常，但是当我从TestMethod调用此方法时，RoomServiceRepository不会返回roomService。我的测试方法如下所示：

[TestClass]
public class InventoryTest
{
    private UnityContainer _container;
    readonly MockObjectsSetup _mos = new MockObjectsSetup();
    private IInventoryService _inventoryService;
    [TestInitialize]
    public void SetupTest()
    {
        _container = new UnityContainer();
        _mos.Setup(_container);
        Config.UnityTestConfig.RegisterTypes(_container);
        _container.RegisterType<IInventoryService, InventoryService>();
        _inventoryService = (InventoryService)_container.Resolve(typeof(InventoryService));
    }
    [TestMethod]
    public void Dont_Change_NotSelected_PriceValues()
    {
        DateTime startDate = DateTime.Parse("6/21/2016");
        DateTime endDate = DateTime.Parse("6/22/2016");
        long roomServiceId = 17;
        InventoryViewModel invViewModel = new InventoryViewModel();
        invViewModel.isUpdatingBoardPrice = invViewModel.isUpdatingPrice = invViewModel.isUpdatingFloatAvailability = true;
        invViewModel.isUpdatingCertainAvailability = false;
        invViewModel.StartDate = startDate;
        invViewModel.EndDate = endDate;
        invViewModel.RoomServiceId = roomServiceId;
        invViewModel.CertainAvailability = 0;
        invViewModel.FloatAvailability = 8;
        var inv = _inventoryService.GetInventory(startDate, endDate, roomServiceId);
        ....
    }
}