code: package io.ray.test;
  
  import io.ray.api.ObjectRef;
  import io.ray.api.Ray;
  import org.testng.Assert;
  import org.testng.annotations.Test;
  
  /** Hello world. */
  public class HelloWorldTest extends BaseTest {
  
    private static String hello() {
      return "hello";
    }
  
    private static String world() {
      return "world!";
    }
  
    private static String merge(String hello, String world) {
      return hello + "," + world;
    }
  
    @Test
    public void testHelloWorld() {
      ObjectRef<String> hello = Ray.task(HelloWorldTest::hello).remote();
      ObjectRef<String> world = Ray.task(HelloWorldTest::world).remote();
      String helloWorld = Ray.task(HelloWorldTest::merge, hello, world).remote().get();
      Assert.assertEquals("hello,world!", helloWorld);
    }
  }
  