code: def test_invalid_method():
      msg = 'method must be "approximate" or "exact", got na'
      assert_raises(
          AttributeError,
          msg,
          permutation_test,
          [1, 2, 3],
          [3, 4, 5],
          lambda x, y: np.mean(x) - np.mean(y),
          method="na",
      )
  
file_path: mlxtend/mlxtend/evaluate/tests/test_permutation.py
imports: import numpy
  from mlxtend.evaluate import permutation_test
  from mlxtend.utils import assert_raises
label_desc: Use image node_id 6 for calling a global function with example usage: test_invalid_method() without return types