Add test assertion helpers

Adds assertions that are not part of Capybara but may be useful to Rails
users writing system tests.

actionpack/lib/system_testing/test_helper.rb

@@ -5,6 +5,7 @@ module SystemTesting
   module TestHelper
     include Capybara::DSL
     include TestHelpers::FormHelper
+    include TestHelpers::Assertions
 
     def after_teardown
       Capybara.reset_sessions!

actionpack/lib/system_testing/test_helpers.rb

@@ -3,5 +3,6 @@ module TestHelpers
     extend ActiveSupport::Autoload
 
     autoload :FormHelper
+    autoload :Assertions
   end
 end

actionpack/lib/system_testing/test_helpers/assertions.rb

+module SystemTesting
+  module TestHelpers
+    module Assertions
+      def assert_all_of_selectors(*items)
+        options = items.extract_options!
+        type = type_for_selector(items)
+
+        items.each do |item|
+          assert_selector type, item, options
+        end
+      end
+
+      def assert_none_of_selectors(*items)
+        options = items.extract_options!
+        type = type_for_selector(items)
+
+        items.each do |item|
+          assert_no_selector type, item, options
+        end
+      end
+
+      private
+        def type_for_selector(*items)
+          if items.first.is_a?(Symbol)
+            items.shift
+          else
+            Capybara.default_selector
+          end
+        end
+    end
+  end
+end