### Question:
BST { public boolean isEmpty() { return root == null; }  int size(); boolean isEmpty(); boolean contains(Key key); Val find(Key key); void put(Key key, Val val); boolean remove(Key key); Key select(int rank); int rank(Key key); Key floor(Key key); Key ceil(Key key);  }### Answer:
@Test public void isEmpty() { Assert.assertEquals(expect.isEmpty(), bst.isEmpty()); }