@Test(timeout = 5000)
public void testEmpty() throws Exception {

  final List<String> empty = new ArrayList<>(0); // empty data
  final InputReader inputReader = generateInputReader(generateCompletableFuture(empty.iterator()));
  // Fetcher
  final ParentTaskDataFetcher fetcher = createFetcher(inputReader);
  assertEquals(Finishmark.getInstance(), fetcher.fetchDataElement());
}