@Override
    public Num calculate(Num price, Num amount) {
        return price.zero();
    }
@Test
    public void calculateBuyPosition() {
        // Holding a bought asset should not incur borrowing costs
        int holdingPeriod = 2;
        Trade entry = Trade.buyAt(0, DoubleNum.valueOf(100), DoubleNum.valueOf(1));
        Trade exit = Trade.sellAt(holdingPeriod, DoubleNum.valueOf(110), DoubleNum.valueOf(1));

        Position position = new Position(entry, exit, new ZeroCostModel(), borrowingModel);

        Num costsFromPosition = position.getHoldingCost();
        Num costsFromModel = borrowingModel.calculate(position, holdingPeriod);

        assertNumEquals(costsFromModel, costsFromPosition);
        assertNumEquals(costsFromModel, DoubleNum.valueOf(0));
    }