Is this JavaScript unit testable using Jasmine?

Is this javascript code unit testable using Jasmine. If not how do we make it unit testable?

The problem basically is the helloworld function is not accessible inside a test spec js file, since it is not in global scope. How do we refactor the code such that it is accessible within the test spec file?

(function($){
    function helloWorld() {
          return "Hello world!";
        }
})(jQuery);