code: def test_to_string():
      var = ExecutionVariables.START_DATETIME
  
      assert var.to_string() == var
  
imports: from __future__ import absolute_import
  import pytest
  from sagemaker.workflow.execution_variables import ExecutionVariables
label_desc: Use image node_id 2 for calling a global function with example usage: test_to_string() without return types