[backport] SI-8689 Make a Future test case determistic

As discussed:

  https://groups.google.com/forum/#!topic/scala-internals/m8I_3GQR4vQ

We need to ensure a happens-before relationship between the callback
that prints "success" and the end of the main method.

1 files changed, 7 insertions, 2 deletions

diff --git a/test/files/jvm/t8689.scala b/test/files/jvm/t8689.scala
index ef43a1df63..3ee20d711a 100644
--- a/test/files/jvm/t8689.scala
+++ b/test/files/jvm/t8689.scala
@@ -4,10 +4,15 @@ object Test {
     import ExecutionContext.Implicits.global
     val source1 = Promise[Int]()
     val source2 = Promise[Int]()
+    val done = Promise[Unit]()
     source2.completeWith(source1.future).future.onComplete {
-      case _ => print("success")
+      case _ =>
+         print("success")
+         done.success(())
     }
     source2.tryFailure(new TimeoutException)
     source1.success(123)
+    import duration._
+    Await.result(done.future, 120.seconds)
   }
-}
\ No newline at end of file
+}