restore helloworld test

Author: sjrd

tests/pos/HelloWorld.scala

@@ -1,15 +1,3 @@
 object HelloWorld {
-  def main(args: Array[String]): Unit = {
-    println("hello world")
-    val list = List(1, 2, 3)
-    list match {
-      case head :: tail => println(head)
-      case Nil => println("empty")
-    }
-    val s = list match {
-      case head :: tail => head.toString
-      case Nil => "empty"
-    }
-    println(s)
-  }
+  def main(args: Array[String]): Unit = println("hello world")
 }