public void CustomerEmptyField()
        {
            customerName        = "Grzegorz";
            customerLastName    = "Kowalski";
            customerNationality = "";
            customerAge         = "15";
            customerPhone       = "543";
            customerAddress     = "Nieznana";

            bool validation = form.AddCustomer(customerName, customerLastName, customerNationality, customerAge, customerPhone, customerAddress);

            Assert.AreEqual(false, validation);
        }