public void add(T value) {
        UUID uuid = value.getUUID();
        if (_map.containsKey(uuid)) {
            throw new AssertionError(String.format("Existing value found with UUID: %s", uuid));
        }
        _map.put(uuid, value);
    }
@Test
    public void addValue() {
        // try adding a new value
        UUIDMap<Value> map = new UUIDMap<>();
        Value value = addNewValue(map);

        // try re-adding the value
        assertThrows(AssertionError.class, () -> map.add(value));

        // try adding a clone of the value
        assertThrows(AssertionError.class, () -> map.add(Cloner.clone(value)));
    }