def test_leftRotationOnRoot(self):
tree = AVLTree()
tree.insert(1)
tree.insert(2)
tree.insert(3)
tree.root = tree.left_rotation(tree.root)
nodes = tree.preorder_traversal()
self.assertEqual(nodes, [2, 1, 3])
def test_leftRotationNoRoot(self):
tree = AVLTree()
tree.left_rotation(tree.root)
nodes = tree.preorder_traversal()
self.assertEqual(nodes, [])
