how to force the routing format being the request one

I am trying to test the mobile way .. using mobile_fu and adding the :mobile format most of my test code is running adding :format => :mobile when necessary, but I wonder how when a controller respond to the :mobile format, the routing can use the request format

In this test case ( contact form) , when the request is coming from a mobile, redirect_to new_contact_url is still using :html

thanks for feedback

  has_mobile_fu   respond_to :html, :mobile, :tablet

  def new     @contact = ContactForm.new()   end

  def create     destination = Rails.configuration.contact_address     @contact = ContactForm.new(subject: I18n.t("mail_form.contact_form_subject"), destination: destination, name: params[:contact_form][:name], email: params[:contact_form] [:email], message: params[:contact_form][:message])     if @contact.save       flash[:notice] = t(:message_send)       @contact = ContactForm.new()       redirect_to new_contact_url     else       render :new     end   end