@Test public void mustBeAbleToUseBuffer() throws Exception { final JavaTestKit probe = new JavaTestKit(system); final List<String> input = Arrays.asList("A", "B", "C"); final CompletionStage<List<String>> future = Source.from(input) .buffer(2, OverflowStrategy.backpressure()) .grouped(4) .runWith(Sink.<List<String>>head(), materializer); List<String> result = future.toCompletableFuture().get(3, TimeUnit.SECONDS); assertEquals(input, result); }