docstr: Test that if Variable key is not present,
  SystemsManagerParameterStoreBackend.get_variables should return None
docstr_tok: ["Test","that","if","Variable","key","is","not","present",",","SystemsManagerParameterStoreBackend.get_variables","should","return","None"]
code: def test_get_variable_non_existent_key(self):
      """
      Test that if Variable key is not present,
      SystemsManagerParameterStoreBackend.get_variables should return None
      """
      secret_id = "airflow/variables/hello"
      create_param = {"Name": secret_id, "SecretString": "world"}
  
      secrets_manager_backend = SecretsManagerBackend()
      secrets_manager_backend.client.create_secret(**create_param)
  
      assert secrets_manager_backend.get_variable("test_mysql") is None
  
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 9 for calling the TestSecretsManagerBackend obj's underlying member method code with example usage: obj.test_get_variable_non_existent_key() without return types