Angular JS testing with external libray like Google Analytics

How do you testing angular controller with external library usage such as google analytic event tracking. For example:

$scope.showVolumn  = function() {
  ga('send', {
    'hitType': 'event',          
    'eventCategory': 'Volume',   
    'eventAction': 'click',      
    'eventLabel': 'Interaction'
  });

  if($scope.native !== 'true')
    vm.showVolumnCtl = !vm.showVolumnCtl;
};

Run thought my test code this error appeard

ReferenceError: Can't find variable: ga

I don't think you can inject ga in the beforeEach right? Any solution i can overcome this?