public void ConvertBalance()
        {
            var balance = new CustomerBalance
            {
                Currency = (int)Currency.GBP,
                Balance  = 1000
            };

            var curr = new CurrencyConverter();
            var res  = curr.ConvertCustomerBalanceToGivenCurrency(balance, Currency.PLN);

            output.WriteLine($"I got {res} PLN from 1000 GBP");
        }