text: describe('last', () => {
      let answer = new Calculator();
      it('should return the last function result and return 2', () => {
          answer.multiplyNum(1, 2);
          let result = answer.last();
          expect(result).toEqual(2);
      });
  });
  
  describe("slot allows the calculator to remember more numbers",() => {
      let answer = new Calculator();
      it("should return 3",()=> {
          answer.addNum(1, 2);
          answer.set_slot(1);
          let result = answer.get_slot(1);
          expect(result).toEqual(3);
      });
  });