public void OnSaleTill_Should_Throw_ArgumentNullException_If_Products_Is_Null()
        {
            IQueryable <Product> products = null;
            DateTime             tillDate = DateTime.Today;

            var ex = Assert.Throws <ArgumentNullException>(() => ProductExtensions.OnSaleTill(products, tillDate));

            Assert.Equal(nameof(products), ex.ParamName);
        }
        public void OnSaleTill_Should_Return_Only_Products_OnSale_And_With_OnSaleTo_Date_Previous_Than_The_Specified_Date()
        {
            var p1 = Product.Create("ean", "sku", "name", "url");
            var p2 = Product.Create("ean", "sku", "name", "url");
            var p3 = Product.Create("ean", "sku", "name", "url");

            p1.SetOnSale(DateTime.Today.AddDays(-5), DateTime.Today.AddDays(-1));
            p2.SetOnSale(DateTime.Today.AddDays(-3), DateTime.Today);

            IQueryable <Product> products = new Product[]
            {
                p1, p2, p3
            }.AsQueryable();
            DateTime tillDate = DateTime.Today;

            var productsOnSale = ProductExtensions.OnSaleTill(products, tillDate).ToArray();

            Assert.True(productsOnSale.All(p => p.IsOnSale && p.OnSaleTo <= tillDate));
        }