public void demonstrateACustomMaterializedValue() throws Exception {
// tests:
RunnableGraph<CompletionStage<Integer>> flow =
Source.from(Arrays.asList(1, 2, 3))
.viaMat(new FirstValue(), Keep.right())
.to(Sink.ignore());
CompletionStage<Integer> result = flow.run(mat);
assertEquals(new Integer(1), result.toCompletableFuture().get(3, TimeUnit.SECONDS));
}