@Test public void mustRepeat() throws Exception { final CompletionStage<List<Integer>> f = Source.repeat(42).grouped(10000).runWith(Sink.<List<Integer>>head(), materializer); final List<Integer> result = f.toCompletableFuture().get(3, TimeUnit.SECONDS); assertEquals(result.size(), 10000); for (Integer i : result) assertEquals(i, (Integer) 42); }