new_contents: from mock import Mock, patch
  import cmemcached
  
  INVALID_SERVER_ADDR = '127.0.0.1:12345'
  
  
  def test_set_multi_return_failure():
      client = cmemcached.Client([INVALID_SERVER_ADDR])
      v = dict([(str(i), "vv%s" % i) for i in range(10)])
      r, failures = client.set_multi(v, return_failure= True)
      assert r == False
      assert failures == v.keys()
  
  
  def test_delete_multi_return_failure():
      client = cmemcached.Client([INVALID_SERVER_ADDR])
      keys = [str(i) for i in range(10)]
      r, failures = client.delete_multi(keys, return_failure= True)
      assert r == False
      assert failures == keys
  
  
  
subject: add a new test file to make sure return_failure parameter work.