public static ProductCatalog BuildCatalog(double price)
 {
     var catalog = new ProductCatalog();
     catalog.Add(new Product(40, true));
     catalog.Add(new Product(60, true));
     catalog.Add(new Product(80, true));
     catalog.Add(new Product(100, true));
     return catalog;
 }
 public SpecificationProductCatalog(ProductCatalog catalog)
 {
     Items = catalog.Items;
 }
 public PredicateProductCatalog(ProductCatalog catalog)
 {
     Items = catalog.Items;
 }
 public BasicProductCatalog(ProductCatalog catalog)
 {
     Items = catalog.Items;
 }