Q:

Unit test function inside jquery

I'm not too familiar with jquery besides the very basics of it, so I might just be missing some terminology when searching for this, but I have a function like the one below, and i'm unable to unit test it. 
$(function () {
    function GetUsers() {
        //does cool stuff to get and return users
    }
}

I've tried stuff like:
it('should get users', function() {
    GetUsers();
});

and even tried naming the jquery function like:
$(function Actions() {
    function GetUsers() {
        //does cool stuff to get and return users
    }
}

and calling Actions. GetUsers() in my unit test, but still not working. 
The error I get is:

ReferenceError: GetUsers is not defined

A:

Your function is declared inside of an anonymous function.  It isn't available in the context of your unit test.  You can either declare it outside of the anonymous function, or set some global field to the function from within it. 
Option 1
var GetUsers = function(){}

$(function(){ 
    ... // use GetUsers somehow 
});

// You can now test GetUsers

Option 2
var someTestableContext = {};

$(function(){ 
    someTestableContext. GetUsers = function(){};
});

// You can now test someTestableContext. GetUsers

Note
You might want to look into scoping, and modularity patterns in javascript.  Your problem doesn't have anything to do with jQuery.