No route matches {:controller=>"submissions"}

I get this error when I'm running a test that simply does get :index. Here is the test code:

  test "should get index" do
    get :index
    assert_response :redirect
    # assert_not_nil assigns(:submissions)
  end

I have a route set up for this controller though in my routes.rb file:

resources :courses do
resources :assignments do
  get 'export', :controller => 'assignments', :action => 'export'
  resources :memberships
  resources :submissions do
    resources :evaluations do
      delete 'destroy', controller: 'reviews', action: 'destroy'
    end
  end

Also, this is what I get for submissions routes when I run rake routes:

              course_assignment_submissions GET    /courses/:course_id/assignments/:assignment_id/submissions(.:format)                                                   submissions#index
                                            POST   /courses/:course_id/assignments/:assignment_id/submissions(.:format)                                                   submissions#create
           new_course_assignment_submission GET    /courses/:course_id/assignments/:assignment_id/submissions/new(.:format)                                               submissions#new
          edit_course_assignment_submission GET    /courses/:course_id/assignments/:assignment_id/submissions/:id/edit(.:format)                                          submissions#edit
               course_assignment_submission GET    /courses/:course_id/assignments/:assignment_id/submissions/:id(.:format)                                               submissions#show
                                            PUT    /courses/:course_id/assignments/:assignment_id/submissions/:id(.:format)                                               submissions#update
                                            DELETE /courses/:course_id/assignments/:assignment_id/submissions/:id(.:format)                                               submissions#destroy

Does anyone know where this error could be coming from then?