code: def unregister_controllers(self):
          
          # TODO(xpconanfan): actually record these errors instead of just
          # logging them.
          for name, module in self._controller_modules.items():
              logging.debug('Destroying %s.', name)
              with expects.expect_no_raises(
                      'Exception occurred destroying %s.' % name):
                  module.destroy(self._controller_objects[name])
          self._controller_objects = collections.OrderedDict()
          self._controller_modules = {}
docs: Destroy controller objects and clear internal registry.
  
          This will be called after each test class.