public void ReturnInt_AttachRemoveCustomersCountIs3() { Item item = new Toy(); Customer Josh = (Customer)item.Attach(new Customer("Josh")); Customer John = (Customer)item.Attach(new Customer("John")); Customer Ben = (Customer)item.Attach(new Customer("Ben")); Customer Jenna = (Customer)item.Attach(new Customer("Jenna")); Customer Christine = (Customer)item.Attach(new Customer("Christine")); item.Detach(Josh); item.Detach(Jenna); int result = item.CustomerCount; result.Should().Be(3); }