public E get(Object o) {
        return map.get(o);
    }
@Test
    public void testGet() {
        ExtendedSet<TestValue> set = new ExtendedSet<>(Maps.newConcurrentMap());
        TestValue e1 = new TestValue("foo", 1);
        set.add(e1);
        TestValue lookupValue = new TestValue("foo", 2);
        TestValue setEntry = set.get(lookupValue);
        assertEquals(e1, setEntry);
    }