### Question:
RadixTreeImpl implements RadixTree<T>, Formattable { public String complete(String prefix) { return complete(prefix, root, ""); } RadixTreeImpl(); T find(String key); boolean delete(String key); void insert(String key, T value); ArrayList<T> searchPrefix(String key, int recordLimit); boolean contains(String key); void visit(String key, Visitor<T, R> visitor); long getSize(); @Deprecated void display(); @Override void formatTo(Formatter formatter, int flags, int width, int precision); String complete(String prefix);  }### Answer:
@Test public void testComplete() { RadixTree<String> trie = new RadixTreeImpl<String>(); trie.insert("apple", "apple"); trie.insert("appleshack", "appleshack"); trie.insert("applepie", "applepie"); trie.insert("applegold", "applegold"); trie.insert("applegood", "applegood"); assertEquals("", trie.complete("z")); assertEquals("apple", trie.complete("a")); assertEquals("apple", trie.complete("app")); assertEquals("appleshack", trie.complete("apples")); assertEquals("applego", trie.complete("appleg")); }