code: def test_node_add_child():
      """Test assignment of child"""
      parent = TreeNode("test")
      child = TreeNode("test")
  
      parent.add_children(child)
  
      assert parent.children[0] is child
      assert child.parent is parent
  
imports: from orion.core.utils.tree import DepthFirstTraversal, PreOrderTraversal, TreeNode, flattened
label_desc: Use image node_id 7 for calling a global function with example usage: test_node_add_child() without return types