Testing subdomains on Rails 3

Hi *, I'm trying to use subdomains on Rails 3, but haven't been able to test the behaviour:

   it “routes ‘http://test.example.com/dashboard’ to UsersController#show with subdomain ‘test’” do
    { :get => ‘http://test.example.com/dashboard’ }.should route_to(
      :controller => ‘users’, :action => ‘show’, :subdomain => ‘test’ )

My route is:

constraints( :subdomain => /.+/ ) do
  match '/dashboard' => 'users#show'

The test fails like this:

   The recognized options <{"action"=>"show", "controller"=>"users"}> did not match <{"action"=>"show", "subdomain"=>"test", "controller"=>"users"}>, difference: <{"subdomain"=>"test"}>

I found many references to this syntax and usage on Google, but even from console the subdomain is only in the request object.
Someone managed to do something like this and can share ?
I've also tried to use subdomain-fu, but no success so far