class ActionController::Renderer

def render(*args)

Render templates with any options from ActionController::Base#render_to_string.
def render(*args)
  raise "missing controller" unless controller
  request = ActionDispatch::Request.new @env
  request.routes = controller._routes
  instance = controller.new
  instance.set_request! request
  instance.set_response! controller.make_response!(request)
  instance.render_to_string(*args)
end