text: const NEXT_PAGE = 'NEXT_PAGE';
  function setNextPageNumber (state={
      all : 1,
      good : 1,
      share : 1,
      ask : 1,
      job : 1
  } , action) {
      switch (action.type) {
          case NEXT_PAGE :
          return Object.assign({} , state , {
              [action.topic] : action.page
          });
          default : 
          return state;
      }
  };
  const pages = {
      all : 1,
      share : 1,
      good : 1,
      ask : 1,
      job : 1
  };
  describe('测试获取下一页页数的reducer' , () => {
      it('应该会获取"share"主题列表的第二页页数' , () => {
          const expectedValue = {
              all : 1,
              good : 1,
              share : 2,
              ask : 1,
              job : 1
          };
          const value = setNextPageNumber(undefined , {
              type : NEXT_PAGE,
              page : ++pages['share'],
              topic : 'share'
          });
          expect(value).toEqual(expectedValue);
      });
      it('应该会获取"good"主题列表的第二个页数' , () => {
          const expectedValue = {
              all : 1,
              good : 2,
              share : 2,
              ask : 1,
              job : 1
          };
          const value = setNextPageNumber({
              all : 1,
              good : 1,
              share : 2,
              ask : 1,
              job : 1
          } , {
              type : NEXT_PAGE,
              topic : 'good',
              page : ++pages['good']
          });
          expect(value).toEqual(expectedValue);
      })
  });