    @Test
    public void testAddChirp() {

        ChirpTopicStub topic = new ChirpTopicStub();
        PersistentEntityTestDriver<ChirpTimelineCommand, ChirpTimelineEvent, NotUsed> driver =
                new PersistentEntityTestDriver<>(system, new ChirpTimelineEntity(topic), "user-1");

        Chirp chirp = new Chirp("user-1", "Hello, world");

        PersistentEntityTestDriver.Outcome<ChirpTimelineEvent, NotUsed> outcome =
                driver.run(new AddChirp(chirp));
        assertEquals(Done.getInstance(), outcome.getReplies().get(0));
        assertEquals(chirp, ((ChirpTimelineEvent.ChirpAdded) outcome.events().get(0)).chirp);
        assertEquals(chirp, topic.chirps.get(0));
        assertEquals(Collections.emptyList(), driver.getAllIssues());
    }