docstr: Test if a default_var is defined and no backend has the Variable,
  the value returned is default_var
docstr_tok: ["Test","if","a","default_var","is","defined","and","no","backend","has","the","Variable",",","the","value","returned","is","default_var"]
code: def test_backend_fallback_to_default_var(self):
      """
      Test if a default_var is defined and no backend has the Variable,
      the value returned is default_var
      """
      variable_value = Variable.get(key="test_var", default_var="new")
      assert "new" == variable_value
  
imports: from __future__ import annotations
  from unittest import mock
  import pytest
  from airflow.configuration import ensure_secrets_loaded, initialize_secrets_backends
  from airflow.models import Connection, Variable
  from airflow.secrets.cache import SecretCache
  from tests.test_utils.config import conf_vars
  from tests.test_utils.db import clear_db_variables
label_desc: Use image node_id 5 for calling the TestVariableFromSecrets obj's underlying member method code with example usage: obj.test_backend_fallback_to_default_var() without return types