const assert = require('assert');

const configs = {
  YEARLY_INTEREST_RATE: 4.0
};

const getSavingsAmount = amount => {
  return amount + amount * (configs.YEARLY_INTEREST_RATE / 100);
};

assert(getSavingsAmount(100) === 104);

configs.YEARLY_INTEREST_RATE = 3.0;

assert(getSavingsAmount(100) === 104);