@Test
  void exists() {
    check(Flowable.fromPublisher(create().exists()).toList().blockingGet()).isOf(false);
    check(Flowable.fromPublisher(create("one").exists()).toList().blockingGet()).isOf(true);
    check(Flowable.fromPublisher(create("one", "two").exists()).toList().blockingGet()).isOf(true);
    check(Flowable.fromPublisher(create("one", "two", "three").exists()).toList().blockingGet()).isOf(true);
  }
Check that correct exceptions are thrown by {@link ReactiveFetcher}
criteria/common/test/org/immutables/criteria/repository/reactive/ReactiveFetcherDelegateTest.java