code: def test_is_valid_prefix_and_sep(
      self, mock_client_callable, mock_get_creds, prefix, sep, is_valid
  ):
      mock_get_creds.return_value = CREDENTIALS, PROJECT_ID
      mock_client = mock.MagicMock()
      mock_client_callable.return_value = mock_client
      backend = CloudSecretManagerBackend()
      backend.connections_prefix = prefix
      backend.sep = sep
      assert backend._is_valid_prefix_and_sep() == is_valid
  
imports: from __future__ import annotations
  import logging
  import re
  from unittest import mock
  import pytest
  from google.api_core.exceptions import NotFound
  from google.cloud.secretmanager_v1.types import AccessSecretVersionResponse
  from airflow.exceptions import AirflowException
  from airflow.models import Connection
  from airflow.providers.google.cloud.secrets.secret_manager import CloudSecretManagerBackend
label_desc: Use image node_id 3 for calling the TestCloudSecretManagerBackend obj's underlying member method code with example usage: obj.test_is_valid_prefix_and_sep(mock_client_callable, mock_get_creds, prefix, sep, is_valid) without return types