public void retrieveOrderItemTest()
{
//Arrange
OrderItemRepository orderItemRepository = new OrderItemRepository();
var expected = new OrderItem(0);
//Assert
//if you compare the 2 objects you'll get a wrong output because they don't refer the same object
//you have to comapre each property
Assert.AreEqual(orderItemRepository.retrieve(0).OrderItemID, expected.OrderItemID);
}