public void payInterest() throws BankException {
SavingsAccount firstAccount = bank.createSavingsAccount(accountNumberOne, interestRate*2);
firstAccount.deposit(depositAmount);
SavingsAccount secondAccount = bank.createSavingsAccount(accountNumberTwo, interestRate);
secondAccount.deposit(depositAmount*2);
bank.payInterest();
assertEquals((int)(depositAmount*(1+(interestRate*2))), firstAccount.balance());
assertEquals((int)(depositAmount*2*(1+interestRate)), secondAccount.balance());
}