开玩笑的@@指标是什么

Question

运行测试时，我会在控制台中看到以下信息

Difference:

    - Expected
    + Received

    @@ -7,11 +7,11 @@
    -   "someField": "foo",
    +   "someField": "bar",

    @@ -25,8 +25,8 @@

    -   "someField": "foo",
    +   "someField": "bar",
      }

@@之间的指示是什么意思？