code: def test_validate_env_vars_vs_existing_env(self):
      # assumes there is at least one existing env var - quite reasonable
      existing_os_env_k, existing_os_env_v = next(
          iter(os.environ.items())
      )
      all_secrets_env_vars = [
          (
              SecretSpec.secret_spec_from_str("t.1", None),
              {"A": "a", existing_os_env_k: existing_os_env_v},
          ),
      ]
      with self.assertRaises(MetaflowException):
          validate_env_vars_vs_existing_env(all_secrets_env_vars)
  
file_path: metaflow/test/unit/test_secrets_decorator.py
imports: import os
  import time
  import unittest
  from unittest.mock import patch
  from metaflow.exception import MetaflowException
  import metaflow.metaflow_config
  from metaflow.plugins.secrets.secrets_decorator import SecretSpec, validate_env_vars_across_secrets, validate_env_vars_vs_existing_env, validate_env_vars, get_secrets_backend_provider
label_desc: Use image node_id 2 for calling the TestEnvVarValidations obj's underlying member method code with example usage: obj.test_validate_env_vars_vs_existing_env() without return types