Vert.x Future onSuccess/onFailure do not propagate errors

VertxFutureTest.java

package testing;

import io.vertx.core.Future;
import io.vertx.core.Promise;
import io.vertx.core.Vertx;

public class VertxFutureTest {
	
	static Object waiter = new Object();
	static boolean done = false;
	
  /**
   * Call with either "a" or "b" as the first argument
   * a) the flow will not complete correctly and will timeout
   * b) the flow will complete correctly and report an error as expected
   **/
	public static void main(String[] args) {
		if (args.length < 1) args = new String[] { "help" };
		switch (args[0]) {
		case "a": testA(); break;
		case "b": testB(); break;
		default:
			System.err.println("Please specify test case to run - 'a' or 'b'");
		}
		System.exit(0);
	}
	
	public static void testA() {
		Promise<Void> event = Promise.promise();
		new Thread(() -> {
			// mimic running the async flow from a thread you don't control, maybe Vert.x event loop

			event.future().onSuccess(__ -> {
				throw new RuntimeException("unexpected error");
			})
			.compose(__ -> Future.succeededFuture()) // another step to run under normal conditions
			.onFailure(t -> System.err.println("Error occured! " + t)) // final error handler
			.eventually(__ -> {
				System.err.println("Done with test");
				finish();
				return Future.succeededFuture();
			});

		}).start();
		
		// cause the event to fire
		event.complete();
		waitForFinish();
	}
	
	public static void testB() {
		Promise<Void> event = Promise.promise();
		new Thread(() -> {
			// mimic running the async flow from a thread you don't control, maybe Vert.x event loop

			event.future().<Void>map(__ -> {
				throw new RuntimeException("unexpected error");
			})
			.compose(__ -> Future.succeededFuture()) // another step to run under normal conditions
			.onFailure(t -> System.err.println("Error occured! " + t)) // final error handler
			.eventually(__ -> {
				System.err.println("Done with test");
				finish();
				return Future.succeededFuture();
			});
			
		}).start();
		
		// cause the event to fire
		event.complete();
		waitForFinish();
	}
	
	static synchronized void finish() {
		synchronized (waiter) {
			done = true;
			waiter.notify();
		}
	}
	
	static void waitForFinish() {
		synchronized (waiter) {
			try {
				waiter.wait(3000);
			} catch (InterruptedException e) {
			}
			if (done) {
				System.out.println("We're done");
			} else {
				System.err.println("Timed out!");
				System.exit(5);
			}
		}
	}
}