Extra test and comment suggested during review

Author: retronym

src/main/scala/scala/concurrent/java8/FutureConvertersImpl.scala

@@ -70,7 +70,7 @@ object FuturesConvertersImpl {
      * @inheritdoc
      *
      * WARNING: completing the result of this method will not complete the underlying
-     *          Scala Future or Promise.
+     *          Scala Future or Promise (ie, the one that that was passed to `toJava`.)
      */
     override def toCompletableFuture(): CompletableFuture[T] = {
       this // TODO or maybe `thenApply(JF.identity())`

src/test/java/scala/compat/java8/FutureConvertersTest.java

@@ -363,4 +363,17 @@ public void testToJavaToCompletableFutureDoesNotMutateUnderlyingPromise() throws
         assertFalse(sf.isCompleted());
         assertFalse(p.isCompleted());
     }
+
+    @Test
+    public void testToJavaToCompletableFutureJavaCompleteCallledAfterScalaComplete() throws ExecutionException, InterruptedException {
+        final Promise<String> p = promise();
+        Future<String> sf = p.future();
+        final CompletionStage<String> cs = toJava(sf);
+        CompletableFuture<String> cf = cs.toCompletableFuture();
+        assertEquals("notyet", cf.getNow("notyet"));
+        p.success("scaladone");
+        assertEquals("scaladone", cf.get());
+        cf.complete("javadone");
+        assertEquals("scaladone", cf.get());
+    }
 }