def test_delete():
splay_tree = SplayTree()
splay_tree.insert(10)
splay_tree.insert(8)
splay_tree.insert(12)
splay_tree.insert(13)
splay_tree.insert(7)
splay_tree.delete(12)
x = splay_tree.pre_order(splay_tree.root(), [])
assert x == [7, 8, 10, 13]
splay_tree.delete(12)
assert x == [7, 8, 10, 13]
