view spec for the create form of a user. it's passing. not using factory_girl and devise. Maybe that's wrong? previous version was webrat syntax. this version is capybara syntax. refactored a bit

new.html.erb_spec.rb

require 'spec_helper'
require 'shared_examples_for_views'

describe "users/new" do
  #generalized method to check a field
  def check_field(form, id, options={})
    field = form.find_field(id)

    options.keys.each do |key|
      field[key].should eq options[key].to_s
    end

  end

let(:user) do
    # mock it? stub it? use factory girl? so many options..
    User.new
    #mock_model(User).as_new_record.as_null_object
  end

  context "with 2 roles present in DB" do
    let(:roles) do
      [create(:admin_role), create(:role)]
    end

    before do
      assign(:user, user)
      #i have to add this, or the roles are not present in DB...
      assign(:roles, roles)

      # stub user as an admin
      # should I do this with devise and factory_girl instead?
      login_user = double('User')
      login_user.stub(:role?).with(:admin).and_return(true)
      controller.stub(:current_user) { login_user }

      render
    end

    # path for cancel and form
    let(:path) { users_path}
    let(:object) { user}

    it_behaves_like "valid form"

    # maybe I should split this up in own tests
    it "renders the user fields" do
      find_form(rendered) do |form|
        check_field(form, "user_login", :type => :text, :name => "user[login]", :placeholder => 'Login')
        check_field(form, "user_firstname", :type => :text, :name => "user[firstname]")
        check_field(form, "user_lastname", :type => :text, :name => "user[lastname]")
        check_field(form, "user_ifxglobalid", :type => :text, :name => "user[ifxglobalid]")

        roles.each do |role|
          check_field(form, "user_role_ids_#{role.id}", :type=> :checkbox, :name => "user[role_ids][]", :value => role.id)
        end
      end
    end

    end
  end

shared_examples_for_views.rb

def find_form(rendered)
  Capybara.string(rendered).find("form").tap do |form|
    yield form
  end
end

shared_examples "valid form" do
  it "should render form" do
    rendered.should have_selector("form[action=\"#{path}\"][method=\"post\"]")
  end

  it "should render submit button" do
    find_form(rendered) do |form|
      input = form.find_button("Create #{object.class.name.capitalize}")
      input[:type] == "submit"
      # submit button
      #form.should have_selector("input[type=\"submit\"]")
    end
  end

  it "should render cancel button" do
    find_form(rendered) do |form|
      # cancel button
      #form.should have_selector("a[href=\"#{path}\"]")
      link = form.find_link("Cancel")
      link[:href] == path
    end
  end
end

Like I commented elsewhere, I don't like to write specs at this level. But I think you're on the right track with using mocks/stubs in this context, since it's more unit test-y. Anything you can do to abstract from Devise in particular at this level is beneficial.