### Question:
RedBlackTree { public V remove(K key) { RedBlackNode<K,V> node = findFirstNode(key); if (node == null) { return null; } V value = node.value; deleteEntry(node); return value; } RedBlackTree(Comparator<K> comparator, boolean allowDuplicateKeys);  RedBlackTree(RedBlackTree<K, V> tree); @Override String toString(); int size(); boolean containsKey(K key); RedBlackNode<K,V> getFirst(); RedBlackNode<K,V> getLast(); RedBlackNode<K,V> lowerBound(K key); RedBlackNode<K,V> upperBound(K key); Pair<RedBlackNode<K, V>, Boolean> put(K key, V value); RedBlackNode<K,V> findFirstNode(K key); RedBlackNode<K,V> findLastNode(K key); V remove(K key); void removeAll(); boolean isEmpty(); void deleteEntry(RedBlackNode<K,V> p); static final String EOL; }### Answer:
@Test public void testRemove() { assertEquals(9, tree.size()); tree.remove(5); assertEquals(8, tree.size()); assertEquals(16, treeWithDups.size()); assertEquals("five",treeWithDups.remove(5)); assertEquals(15, treeWithDups.size()); assertEquals("five-a",treeWithDups.remove(5)); assertEquals(14, treeWithDups.size()); assertEquals("five-b",treeWithDups.remove(5)); assertEquals(13, treeWithDups.size()); assertEquals("five-c",treeWithDups.remove(5)); assertEquals(12, treeWithDups.size()); assertNull(treeWithDups.remove(5)); assertEquals(12, treeWithDups.size()); }