code: def test_node_add_children():
      """Test assignment of children"""
      parent = TreeNode("test")
      child1 = TreeNode("test1")
      child2 = TreeNode("test2")
  
      parent.add_children(child1, child2)
  
      assert parent.children[0] is child1
      assert parent.children[1] is child2
      assert child1.parent is parent
      assert child2.parent is parent
  
imports: from orion.core.utils.tree import DepthFirstTraversal, PreOrderTraversal, TreeNode, flattened
label_desc: Use image node_id 9 for calling a global function with example usage: test_node_add_children() without return types