@Override
    public boolean putIfAbsent(K key, V value) {
        return map.putIfAbsent(key, value) == null;
    }
@Test
    public void testPutIfAbsent() {
        map.put(42, "oldValue");

        assertTrue(adapter.putIfAbsent(23, "newValue"));
        assertFalse(adapter.putIfAbsent(42, "newValue"));

        assertEquals("newValue", map.get(23));
        assertEquals("oldValue", map.get(42));
    }