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: 
I know this is an old topic, but in my case expiring cookies was necessary so here's a solution that combines the above answers and a `setTimeout` call to expire cookies after `X` seconds:

```
const fakeCookies = {
    // cookie jar
    all: {},

    // timeouts
    timeout: {},

    // get a cookie
    get: function(name)
    {
        return this.all[ name ]
    },

    // set a cookie
    set: function(name, value, expires_seconds)
    {
        this.all[ name ] = value;

        if ( expires_seconds ) {
            ! this.timeout[ name ] || clearTimeout( this.timeout[ name ] )
            this.timeout[ name ] = setTimeout(() => this.unset(name), parseFloat(expires_seconds) * 1000)
        }
    },

    // delete a cookie
    unset: function(name)
    {
        delete this.all[ name ]
    }    
}

```
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!!