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);
}