TransformingObservables { @NonNull public static Observable<Integer> sequential() { Observable<Integer> first = Observable.just(1, 4, 8); Observable<Integer> second = Observable.just(2, 6, 9); Observable<Integer> third = Observable.just("Red", "Hello").map(String::length); return Observable.concat(first, second, third); }  @NonNull static Observable<Integer> sequential(); @NonNull static Observable<Integer> parallel(); @NonNull static Observable<Person> zipPersons();  }
@Test public void testSequential() throws Exception { assertNotNull(TransformingObservables.sequential()); }