@Override
    @ManagedOperation(description = "Adds the key to the store")
    public boolean add(String key) {
        return cache.putIfAbsent(key, false) == null;
    }
@Test
    void testAdd() {
        // add first key
        assertTrue(repo.add(key01));
        assertTrue(cache.containsKey(key01));

        // try to add the same key again
        assertFalse(repo.add(key01));

        // try to add an other one
        assertTrue(repo.add(key02));
        assertTrue(cache.containsKey(key02));
    }