private void btnAddCustomer_Click(object sender, EventArgs e)
        {
            AddCustomerForm dialoge = new AddCustomerForm();

            if (DialogResult.OK == dialoge.ShowDialog())
            {
                Customer createdCust = dialoge.newCustomerreturn();
                createdCust.ReadLastCustNum(customerList.Data());
                customerList.AddNewCustomer(createdCust);
            }

            UpdateDataGrid();
        }
        public void Customer_ReadLastcustNum_Pos()
        {
            try
            {
                // arrange
                Customer     customer     = new Customer("Florian", "Binder", "*****@*****.**");
                CustomerList customerList = new CustomerList();
                customerList.ReadCustomerList();

                //act
                customer.ReadLastCustNum(customerList.Data());
                Assert.IsTrue(customer.CustNum >= 10000);
            }
            catch (Exception ex)
            {
                Assert.Fail();
                return;
            }
        }
        public void CustomerList_AddCustomer_Pos()
        {
            try
            {
                // arrange
                Customer     customer     = new Customer("Flo", "Binder", "*****@*****.**");
                CustomerList customerList = new CustomerList();
                customerList.ReadCustomerList();
                customer.ReadLastCustNum(customerList.Data());

                //act
                customerList.AddNewCustomer(customer);
            }
            catch (Exception ex)
            {
                Assert.Fail();
                return;
            }
        }
        public void Customer_ChangeCustomerinList_Pos()
        {
            try
            {
                // arrange

                CustomerList customerList = new CustomerList();
                customerList.ReadCustomerList();
                Customer customer = customerList.Data()[0];
                customer.ChangeLastName = "Biiiinnndder";

                //act
                customerList.ChangedCustomer(customer);
            }
            catch (Exception ex)
            {
                Assert.Fail();
                return;
            }
        }