public void remove() {
      if( _prevV == null ) throw new IllegalStateException();
      _sschm.putIfMatch( _prevK, TOMBSTONE, _prevV ); // !!! tries to match with old value
      _prevV = null;
    }

    private void testKeySetIteratorRemoveKeyAfterValChange(Map<Long, String> map, Long testKey) {
        map.put(testKey, "0");
        assertEquals("0", map.get(testKey));
        assertEquals(1, map.size());
        assertTrue(!map.isEmpty());
        assertTrue(map.containsKey(testKey));
        assertTrue(map.containsValue("0"));
        Iterator<Long> iterator = map.keySet().iterator();
        map.put(testKey, "1");
        
        while (iterator.hasNext()) {
            long key = iterator.next();
            if (key == testKey) {
                iterator.remove(); // !!! current impl does not remove the key !!!
                break;
            }
        }
        assertEquals(null, map.get(testKey));
        assertEquals(0, map.size());
        assertTrue(map.isEmpty());
        assertTrue(!map.containsKey(testKey));
        assertTrue(!map.containsValue("1"));
    }