Set requests' header inside spec/routing

I'm working on a Rails application having a REST API in JSON format and
versioned (according to this excellent Ryan's cast:

For instance, there is a spec/requests spec:

  require 'spec_helper'

  describe "My Friends" do
    describe "GET /my/friends.json" do
      it "should get my_friends_path" do
        get v1_my_friends_path, {}, {'HTTP_ACCEPT' =>
'application/vnd.myapp+json; level=1'}
        response.status.should be(401)

And it works well.
But (keeping this example) how can we write the routing spec? For
instance this spec isn't correct:

  require 'spec_helper'

  describe "friends routing" do
    it "routes to #index" do
      get("/my/friends.json", nil, {'HTTP_ACCEPT' =>
'application/vnd.myapp+json; level=1'}).
        should route_to({ action: "index",
                      controller: "api/v1/private/my/friends",
                          format: "json" })

...because `get` can take only 1 param.

I tried different ways (such as with request.headers['Accept'] or
@request.headers['Accept']... where request is undefined and @request is
nil). I really don't see how to do.

I'm on Ruby 1.9.3, Rails 3.2.6 and rspec-rails 2.11.0. Thanks.