public function getInterestAmount($amount, $installmentQuantity)
    {
        $minimumAmountNoInterest = $this->getMinimumAmountNoInterest($installmentQuantity);

        if (
            ($minimumAmountNoInterest === null) ||
            ($minimumAmountNoInterest !== null) && ($amount < $minimumAmountNoInterest)
        ) {
            $interestRateForInstallment = $this->getInterestRateForInstallment($installmentQuantity);
        } else {

            $interestRateForInstallment = 1;
        }

        $totalInstallmentAmount = $interestRateForInstallment * $amount;
        return ($totalInstallmentAmount - $amount);
    }