以下のコードで商品ID 456を指定した場合の返り値は何になりますか？ ```ruby stock_service = instance_double(StockService) allow(stock_service).to receive(:fetch_stock_quantity).with(123).and_return(50) allow(stock_service).to receive(:fetch_stock_quantity).with(456).and_return(10) result = stock_service.fetch_stock_quantity(456) ```
