public void addToStock_Test()
{
var product = new Product(5, "prod1", 10, "kg", 0.3);
itemsInStock.addToStock(product);
var available = itemsInStock.isAvailable(5);
var productResult = itemsInStock.getProduct(5);
Assert.AreEqual(product, productResult);
Assert.AreEqual(available, true);
}