docstr: Test that if Config key is not present in AWS Secrets Manager,
  SecretsManagerBackend.get_config should return None,
  SecretsManagerBackend._get_secret should not be called
docstr_tok: ["Test","that","if","Config","key","is","not","present","in","AWS","Secrets","Manager",",","SecretsManagerBackend.get_config","should","return","None",",","SecretsManagerBackend._get_secret","should","not","be","called"]
code: def test_config_prefix_none_value(self, mock_get_secret):
      """
      Test that if Config key is not present in AWS Secrets Manager,
      SecretsManagerBackend.get_config should return None,
      SecretsManagerBackend._get_secret should not be called
      """
      kwargs = {"config_prefix": None}
  
      secrets_manager_backend = SecretsManagerBackend(**kwargs)
  
      assert secrets_manager_backend.get_config("config") is None
      mock_get_secret.assert_not_called()
  
imports: from __future__ import annotations
  import json
  from unittest import mock
  import pytest
  from moto import mock_secretsmanager
  from airflow.providers.amazon.aws.secrets.secrets_manager import SecretsManagerBackend
label_desc: Use image node_id 13 for calling the TestSecretsManagerBackend obj's underlying member method code with example usage: obj.test_config_prefix_none_value(mock_get_secret) without return types