old_contents: from unittest.mock import call
  
  
  def calls_from(list_args):
      return [call(*args) for args in list_args]
  
new_contents: from mock import call
  
  
  def calls_from(list_args):
      return [call(*args) for args in list_args]
  
subject: Load mock module from mock package instead of unittest to support Python prior to 3.3