code: def test_parallel_walk_string_leaves(self):
      src = """
        def f(a):
          global g
      """
      node = parser.parse(textwrap.dedent(src))
      for child_a, child_b in ast_util.parallel_walk(node, node):
          self.assertEqual(child_a, child_b)
  
imports: import ast
  import collections
  import textwrap
  import gast
  from tensorflow.python.autograph.pyct import anno
  from tensorflow.python.autograph.pyct import ast_util
  from tensorflow.python.autograph.pyct import loader
  from tensorflow.python.autograph.pyct import parser
  from tensorflow.python.autograph.pyct import pretty_printer
  from tensorflow.python.autograph.pyct import qual_names
  from tensorflow.python.platform import test
label_desc: Use image node_id 20 for calling the AstUtilTest obj's underlying member method code with example usage: obj.test_parallel_walk_string_leaves() without return types