let request specs use integration test services

Rails integration tests have services like assert_select.
This makes them available in request specs.

Author: bronson

lib/rspec/rails/example/request_example_group.rb

@@ -1,5 +1,14 @@
 module RSpec
   module Rails
+    # Raises an error if the user tries to call integration test helpers.
+    # If the helpers are available then this module will be ignored.
+    module IntegrationHelperWarnings
+      extend ActiveSupport::Concern
+      [:assert_select, :url_for, :url_options].each do |name|
+        define_method(name) { |*| raise "you must upgrade Rails to call #{name}" }
+      end
+    end
+
     # @api public
     # Container class for request spec functionality.
     module RequestExampleGroup
@@ -11,6 +20,12 @@ module RequestExampleGroup
       include RSpec::Rails::Matchers::RenderTemplate
       include ActionController::TemplateAssertions
 
+      begin
+        include ActionDispatch::IntegrationTest::Behavior
+      rescue NameError
+        include IntegrationHelperWarnings
+      end
+
       # Delegates to `Rails.application`.
       def app
         ::Rails.application