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
