Found the magic incantation for devise controller specs.

spec/controllers/registrations_controller_spec.rb

+#   Copyright (c) 2010, Diaspora Inc.  This file is
+#   licensed under the Affero General Public License version 3 or later.  See
+#   the COPYRIGHT file.
+
+require File.join(File.dirname(__FILE__), "..", "spec_helper")
+
+describe RegistrationsController do
+  include Devise::TestHelpers
+
+  render_views
+
+  before do
+    request.env["devise.mapping"] = Devise.mappings[:user]
+  end
+
+  describe "#new" do
+    it "succeeds" do
+      get :new
+      response.should be_success
+    end
+  end
+end