@Override
    public boolean remove(Object o) {
        return map.remove(o) != null;
    }
@Test
    public void testRemoveFailure() {
        ExtendedSet<TestValue> set = new ExtendedSet<TestValue>(Maps.newConcurrentMap());
        TestValue val = new TestValue("foo", 1);
        assertFalse(set.remove(val));
    }