def amount_ok?( order_amount, order_discount = BigDecimal.new( '0.0' ) )
      BigDecimal.new( gross ) == order_amount && BigDecimal.new( discount.to_s ) == order_discount
    end
def amount_ok?( order_amount, order_discount = BigDecimal.new( '0.0' ) )
      BigDecimal.new( gross ) == order_amount && BigDecimal.new( discount.to_s ) == order_discount
    end
Order amount should be equal to gross - discount