def test_set_parent_twice(self):
node1, node2, node3 = TreeNode(), TreeNode(), TreeNode()
node1.parent = node2
node1.parent = node3
assert node2.children == []
assert node3.children == [node1, ]
def test_set_parent(self):
node1, node2 = TreeNode(), TreeNode()
node1.parent = node2
assert node1.parent == node2
assert node2.children == [node1, ]
