new_contents: from __future__ import absolute_import
  from __future__ import division
  from __future__ import unicode_literals
  
  from testtools import matchers
  
  class MatchesInvocation(matchers.MatchesListwise):
      """
      Matches an invocation recorded by :class:`unittest.mock.Mock.call_args`
  
      Args:
          *args: Matchers matching the recorded parameter at the same position.
          **kwds: Matchers matching the recorded keyword parameter with the same
              key.
      """
      def __init__(self, *args, **kwds):
          super(MatchesInvocation, self).__init__([
              matchers.MatchesListwise(args),
              matchers.MatchesDict(kwds)
          ])
  
subject: Add a custom testtools matcher for verifying invocations