code: def test_parent_prefix(self):
      parent = counting.Counter(prefix="parent")
      child = counting.Counter(parent, prefix="child", time_delta=0.0)
      self.assertEqual(child.get_steps_key(), "child_steps")
  
file_path: acme/acme/utils/counting_test.py
imports: import threading
  from acme.utils import counting
  from absl.testing import absltest
label_desc: Use image node_id 6 for calling the CountingTest obj's underlying member method code with example usage: obj.test_parent_prefix() without return types