long balance = 1000;
float interest = 3.3f;
String accountNumber = "123";
bank.erzeuge_spar_konto(accountNumber, interest);
Konto konto = bank.finde(accountNumber);
konto.einzahlen(balance);
assertEquals(balance, konto.kontostand());
bank.verzinsen();
balance += (long)(balance*interest)/100;
assertEquals(balance, konto.kontostand());
bank.verzinsen();