Dependency injection for an another library in requires

ajax.js

module.exports = function(library){
  var get = function(url, callback){
    library.some_get_fn(url, 'additional param', callback);  
  };
  
  return {
    get: get
  };
};

ajax_spec.js

var dummy_lib = {
  some_get_fn: function(url, additional_param, callback){
    
  }
};
var ajax = require('ajax')(dummy_lib);

it('calls out to dummy lib fn', function(){
  spyOn(dummy_lib, 'some_get_fn');
  ajax.get('foo', function(){});
  expect(dummy_lib.some_get_fn).toHaveBeenCalled();
});

parent.js

var ajax_lib = require('some-ajax-library');
var ajax = require('ajax')(ajax_lib);

ajax.get('/thing.json', function(){
  console.log('!');
});