public void ReturnCustomer_WhenCustomerIDIsFound()
            {
                CustomerBase customerBase = new CustomerBase();

                customerBase.Add(new Customer("Joey", 1121));
                customerBase.Add(new Customer("Jordan", 9999));
                customerBase.Add(new Customer("Jacob", 2223));
                Assert.IsNotNull(customerBase.Find(1121));
                Assert.IsNotNull(customerBase.Find(9999));
                Assert.IsNotNull(customerBase.Find(2223));
            }
            public void ReturnNull_WhenCustomerIDIsNotFound()
            {
                CustomerBase customerBase = new CustomerBase();

                customerBase.Add(new Customer("Jackson", 1234));
                customerBase.Add(new Customer("Roger", 5678));
                Assert.IsNull(customerBase.Find(3333));
            }