Testing asynchronous code.

Test.java

import org.junit.BeforeClass;
import org.junit.Test;
import org.vertx.java.core.Handler;
import org.vertx.java.core.Vertx;
import org.vertx.java.deploy.impl.VertxLocator;

public class PromiseTests {

  private Object lock = new Object();

  @BeforeClass
  public static void environment() {
    VertxLocator.vertx = Vertx.newVertx();
  }

  public Promise<Object> makePromise() {
    final Promise<Object> promise = new Promise<>();

    VertxLocator.vertx.runOnLoop(new Handler<Void>() {
      @Override
      public void handle(Void event) {
        System.out.print("Working.");
        for (int i = 0; i < 10; i++) {
          System.out.print(".");

          try {
            Thread.sleep(200);
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }

        System.out.println();
        promise.fulfill("Hello World");
      }
    });

    return promise;
  }

  @Test
  public void basic() throws Exception {
    runTest(new Runnable() {
      @Override
      public void run() {
        makePromise()
            .then(new PromiseHandler<Void>() {
              @Override
              public Void handle() {
                System.out.println("Wish granted");
                endTest();
                return null;
              }
            });
      }
    });
  }

  @Test
  public void chain() throws Exception {
    runTest(new Runnable() {
      @Override
      public void run() {
        makePromise()
            .then(new PromiseHandler<Void>() {
              @Override
              public Void handle() {
                System.out.println("Wish granted");
                return null;
              }
            })
            .then(new PromiseHandler<Void>() {
              @Override
              public Void handle() {
                System.out.println("What shall I do with my wish?");
                endTest();
                return null;
              }
            });
      }
    });
  }

  private void waitTest() throws InterruptedException {
    synchronized (lock) {
      lock.wait();
    }
  }

  private void endTest() {
    synchronized (lock) {
      lock.notifyAll();
    }
  }

  private void runTest(Runnable runnable) throws InterruptedException {
    new Thread(runnable).start();
    waitTest();
  }
}