@Override
    public boolean isEmpty() {
        return items.isEmpty();
    }
@Test
    public void testIsEmpty() throws Exception {
        //Checks empty condition
        //asserts that the map starts out empty
        assertTrue("Map should be empty", map.isEmpty());
        map.put(1, 1);
        assertFalse("Map shouldn't be empty.", map.isEmpty());
        map.remove(1);
        assertTrue("Map should be empty", map.isEmpty());
    }