How to Efficiently Wait for RxJava Observer to Complete?

Almost all tutorials including the RxJava official ones deliver a message to RxJava developers that Thread.sleep(...) is recommended in testing RxJava code snippets. However, that is not efficient enough.

Here is an alternative way for your reference.

AtomicBoolean atomicBoolean = new AtomicBoolean(false);
ExecutorService executorService = Executors.newFixedThreadPool(4);
Observable.timer(10, TimeUnit.MILLISECONDS, Schedulers.from(executorService))
        .subscribe(t -> atomicBoolean.set(true));
executorService.awaitTermination(100, TimeUnit.MILLISECONDS);
assertTrue(atomicBoolean.get());

The key is to inject a custom thread pool and wait for that thread pool to complete.