https://blogs.sap.com/2015/01/05/abap-test-double-framework-an-introduction/
1: 创建接口ZIF_TD_CURRENCY_CONVER

2:添加,事件和方法
interface ZIF_TD_CURRENCY_CONVER
public .
EVENTS new_currency_code EXPORTING VALUE(currency_code) TYPE string.
METHODS convert
IMPORTING
amount TYPE i
source_currency TYPE string
target_currency TYPE string
RETURNING VALUE(result) TYPE i
RAISING cx_td_currency_exception.
METHODS convert_to_base_currency
IMPORTING
amount TYPE i
source_currency TYPE string
EXPORTING
base_currency TYPE string
base_curr_amount TYPE i.
endinterface.
3:创建一个类

为该类创建测试类
