Javascript Unit testing and refactoring (using Angular js framework)

I (as a js/ng newbie) wanna know how do I start on my unit-test journey for the following angular code (Controller with some functions) and mocking necessary? Would appreciate beautiful suggestions. Thanks

    angular.module('HelloWorld')
.controller('myCtrl', function ($scope, firstService, secondService, messageService) {

    'use strict';

    function goWhereTheWindBlows() { // some implementation }

    $scope.mainFun = function(var1) {

        firstService.showSomething(var1, function() {
            var result = secondService.read(var1); 
            // result is the result of http get (200 or 400)
            extracted(result);
        }, goWhereTheWindBlows);

        function extracted(result) {
            result.then(function () {
                messageService.addMessage({ message: 'Success', type: 'standard' });
            }, function () {
                messageService.addMessage({ message: 'Failure', type: 'error' });
            });
        }
    };
 });