### Question:
Part1CreationTransformationTermination { @Complexity(EASY) public static Observable<String> mapToString(Observable<Long> input) { throw new RuntimeException("Not implemented"); }  @Complexity(EASY) static Observable<String> justABC(); @Complexity(EASY) static Observable<String> fromArray(String... args); @Complexity(EASY) static Observable<String> error(Throwable t); @Complexity(EASY) static Observable<Integer> convertNullableValueToObservable(@Nullable Integer nullableElement); @Complexity(EASY) static Observable<String> deferCalculation(Func0<Observable<String>> calculation); @Complexity(EASY) static Observable<Long> interval(long interval, TimeUnit timeUnit); @Complexity(EASY) static Observable<String> mapToString(Observable<Long> input); @Complexity(EASY) static Observable<String> findAllWordsWithPrefixABC(Observable<String> input); @Complexity(MEDIUM) static Observable<String> fromFutureInIOScheduler(Future<String> future); @Complexity(MEDIUM) static void iterateNTimes(int times, AtomicInteger counter); @Complexity(MEDIUM) static Observable<Character> flatMapWordsToCharacters(Observable<String> input);  }### Answer:
@Test public void mapToStringTest() { mapToString(Observable.just(1L, 2L, 3L, 4L)) .test() .assertValues("1", "2", "3", "4") .assertCompleted() .awaitTerminalEvent(); }