Unit testing of Services / Factories - AngularJS - Jasmine

I have some troubles writing tests for my services in my angularJS project. I am using Karma and Jasmine for my unit tests. To begin, I chose a service with no dependencies, but I never had passed the tests.

Here's my service ( written with coffeeScript )

angular.module('app').factory 'rankFactory', [ ->
  rankFactory = {}
  ranks = [
    {
      id: 0
      label: 'RANK0'
    }
    {
      id: 1
      label: 'RANK1'
    }
  ]

  rankFactory.getRanks = ->
    ranks

  rankFactory.getRanks = (id) ->
    ranks[id]

  rankFactory
 ]

The service works fine. Thus, the test doesn't. Here's my test :

describe('rank Factory unit tests', function(){
    describe  ('when I call myService rankFactory.getRanks ()', function() {

        beforeEach(module('app'));

            it('returns ranks', inject(function(rankFactory){
                expect(rankFactory.getRanks()).not.to.equal(null);
            }))
        }
    )
});

I have been trying for multiple hours, and read a lot of issues and documentation but still can not find out why it doesn't work. Can you help me please?