Question: `document.cookie` is like a string, but it is not a string. To quote the example from the [Mozilla doc](https://developer.mozilla.org/En/Document.cookie):

```
document.cookie = "name=oeschger";
document.cookie = "favorite_food=tripe";
alert(document.cookie);
// displays: name=oeschger;favorite_food=tripe

```

If you tried to make a mock cookie using only a string, you would *not* get the same results:

```
var mockCookie = "";
mockCookie = "name=oeschger";
mockCookie = "favorite_food=tripe";
alert(mockCookie);
// displays: favorite_food=tripe

```

So, if you wanted to unit test a module that operates on the cookie, and if you wanted to use a mock cookie for those tests, could you? **How?**

Answer: 
Here is how I ended up doing it in Jest:

My cookie wasn't added anymore to `document.cookie` after adding the `Secure` attribute (because `document.location` is the insecure `http://localhost`).

So after lots of trials and errors *(trying to intercept `document.cookie`'s setter and dropping its `;Secure` from it, but then calling again `document.cookie =`  with the new value triggered an infinite loop as it entered again the setter...)*, I ended up with this quite simple solution:

```js
beforeEach(function() {
  let cookieJar = document.cookie;
  jest.spyOn(document, 'cookie', 'set').mockImplementation(cookie => {
    cookieJar += cookie;
  });
  jest.spyOn(document, 'cookie', 'get').mockImplementation(() => cookieJar);
})

```
Personally i was unable to hijack the document object.
A simple solution which seems to work for me was the following...

At the top of my test script i define a fakeCookie object:

```
var fakeCookie = {
    cookies: [],
    set: function (k, v) {
        this.cookies[k] = v;
    },
    get: function (k) {
        return this.cookies[k];
    },
    reset: function () {
        this.cookies = [];
    }
};

```

Then in my beforeEach() i define my cookie stub. This basically intercepts calls to jQuery.cookie and (instead!) call the callback function that i have defined (see below):

```
beforeEach(function() {
    var cookieStub = sinon.stub(jQuery, "cookie", function() {
        if (arguments.length > 1) {
            fakeCookie.set(arguments[0], arguments[1]);
        }
        else {
            return fakeCookie.get(arguments[0]);
        }
    });
});

```

Any time that i get or set a cookie value it uses my fakeCookie instead of the real jQuery.cookie. It does this by looking at the number of parameters passed and deduces whether its a get/set. I literally pasted this in and it all worked straight off the bat.
Hope this helps!!