code: def test_flatten(self):
      assert (
          tuple(
              argmap._flatten([[[[[], []], [], []], [], [], []]], set())
          )
          == ()
      )
  
      rlist = ["a", ["b", "c"], [["d"], "e"], "f"]
      assert "".join(argmap._flatten(rlist, set())) == "abcdef"
  
imports: import os
  import pathlib
  import random
  import tempfile
  import pytest
  import networkx
  from networkx.utils.decorators import argmap, not_implemented_for, np_random_state, open_file, py_random_state
  from networkx.utils.misc import PythonRandomInterface
label_desc: Use image node_id 9 for calling the TestArgmap obj's underlying member method code with example usage: obj.test_flatten() without return types