java如何测试返回值是否正确

Question

我必须为下面的课程做jUnit测试。我想在方法使用后测试返回值是否正确。我坐了两个小时，在谷歌和这里寻求帮助。有人能帮忙给点建议吗？或者它应该是什么样子

@Service
public class CurrencyToDBImpl implements CurrencyToDB
{

    @Override
    public ArrayList<CurrencyValue> createCurrencyListToDB(List<CurrencyRateList> list)
    {
        ArrayList<CurrencyValue> currencyArrayList = new ArrayList<>();
        List<Rate> rateList = list.get(0).getRates();

        rateList.forEach(rate -> {
            if(rate.getCode().equals("USD") || rate.getCode().equals("GBP") ||
               rate.getCode().equals("EUR") || rate.getCode().equals("AUD"))
            {
                currencyArrayList.add(new CurrencyValue(rate.getMid(), rate.getCode(), rate.getCurrency()));
            }
        });

        return currencyArrayList;
    }
}