code: def test_descendants():
      """test the get_descendants() method"""
      sf = simple_forest()
      assert sf.get_descendants(0) == [0]
      assert sf.get_descendants(1) == [1]
      assert sf.get_descendants(2) == [0, 1, 2]
      assert sf.get_descendants(4) == [0, 1, 2, 3, 4]
  
file_path: nipy/nipy/algorithms/graph/tests/test_forest.py
imports: import numpy
  from ..forest import Forest
label_desc: Use image node_id 5 for calling a global function with example usage: test_descendants() without return types