### Question:
MultiFirstPublisher extends CompletionSingle<T> { @Override public void subscribe(Flow.Subscriber<? super T> subscriber) { source.subscribe(new FirstSubscriber<>(subscriber)); } MultiFirstPublisher(Multi<T> source); @Override void subscribe(Flow.Subscriber<? super T> subscriber);  }### Answer:
@Test public void error() { TestSubscriber<Object> ts = new TestSubscriber<>(); Multi.error(new IOException()) .first() .subscribe(ts); ts.assertFailure(IOException.class); }