@Test
public void emptyXMap() {

    TestObserver<Integer> to = new TestObserver<Integer>();
    assertTrue(ObservableScalarXMap.tryScalarXMapSubscribe(new EmptyCallablePublisher(), to, new Function<Integer, ObservableSource<Integer>>() {
        @Override
        public ObservableSource<Integer> apply(Integer f) throws Exception {
            return Observable.just(1);
        }
    }));
    to.assertResult();
}