old_contents: import abc
  
  import six
  
  
  @six.add_metaclass(abc.ABCMeta)
  class BaseBackend(object):
  
      @abc.abstractmethod
      def setup_instance(self):
          """Called by setUpClass to setup an instance"""
  
      @abc.abstractmethod
      def cleanup(self):
          """Needs to cleanup the resources created in ``setup_instance``"""
  
new_contents: # Copyright 2015 Cloudbase Solutions Srl
  # All Rights Reserved.
  #
  #    Licensed under the Apache License, Version 2.0 (the "License"); you may
  #    not use this file except in compliance with the License. You may obtain
  #    a copy of the License at
  #
  #         http://www.apache.org/licenses/LICENSE-2.0
  #
  #    Unless required by applicable law or agreed to in writing, software
  #    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
  #    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
  #    License for the specific language governing permissions and limitations
  #    under the License.
  
  import abc
  
  import six
  
  
  @six.add_metaclass(abc.ABCMeta)
  class BaseBackend(object):
  
      @abc.abstractmethod
      def setup_instance(self):
          """Called by setUpClass to setup an instance"""
  
      @abc.abstractmethod
      def cleanup(self):
          """Needs to cleanup the resources created in ``setup_instance``"""
  
subject: Add the license header where it's missing.