@Test
  void basic() {
    Flowable<WatchEvent<Person>> flowable = Flowable.fromPublisher(repository.watcher(person).watch());
    TestSubscriber<WatchEvent<Person>> test = flowable.test();
    repository.insert(generator.next().withId("id1").withFullName("p1"));
    test.awaitCount(1).assertValueCount(1);
    test.assertNotComplete();
    WatchEvent<Person> event = test.values().get(0);
    check(event.key()).is("id1");
    check(event.operation()).is(WatchEvent.Operation.INSERT);
    check(event.newValue().isPresent());
    check(event.newValue().get().id()).is("id1");
    check(event.newValue().get().fullName()).is("p1");
  }
Checks if current mongo cluster has <a href="https://www.mongodb.com/docs/manual/replication/">replication</a> enabled.
Change Streams only work with replication enabled.
criteria/mongo/test/org/immutables/criteria/mongo/ChangeStreamsTest.java