Spying on Backbone.js route calls with Jasmine

Having problems spying method calls on a Backbone Router to ensure it calles the right method on a given route.

excerpt from the test

describe 'Router', ->
    beforeEach ->
        @router = new App.Router()
        Backbone.history.start()

    afterEach ->
        Backbone.history.stop()

    describe 'routes', ->
         it 'should be defined', ->
              expect(@router.routes).toBeDefined()

         describe 'default route', ->
             it 'should be defined', ->
                  expect(@router.routes['']).toBeDefined()

             it 'should call index', ->
                 spy = spyOn(@router, "index")
                 @router.navigate('', true)
                 expect(spy).toHaveBeenCalled()

The router

class App.Router extends Backbone.Router
    routes:
        '' : 'index'

    index: ->
        console.log "router.index has been called"

Everything passes except the last test "should call index". It fails with the message "Expected spy index to have been called". Ive tried other variants

it "should call index", ->
    spyOn(@router, "index")
    @router.navigate('', true)
    expect(@router.index).toHaveBeenCalled()

I can also see the "router.index has been called" log output in the test output from the original Router.index function

Thanks!

EDIT: One solution

describe '#1 Solution', ->
    it 'should call index', ->
        spyOn(App.Router.prototype, "index")
        @router = new App.Router()
        Backbone.history.start()
        @router.navigate('', true)
        expect(App.Router.prototype.index).toHaveBeenCalled()