code: def mutate(context):
      
      try:
          result = parse(context.source, error_recovery=False)
      except Exception:
          print('Failed to parse %s. Internal error from parso follows.' % context.filename)
          print('----------------------------------')
          raise
      mutate_list_of_nodes(result, context=context)
      mutated_source = result.get_code().replace(' not not ', ' ')
      if context.remove_newline_at_end:
          assert mutated_source[-1] == '\n'
          mutated_source = mutated_source[:-1]
      if context.number_of_performed_mutations:
          # If we said we mutated the code, check that it has actually changed
          assert context.source != mutated_source
      context.mutated_source = mutated_source
      return mutated_source, context.number_of_performed_mutations
docs: :type context: Context
      :return: tuple: mutated source code, number of mutations performed
      :rtype: tuple[str, int]