### Question:
ScreenStack extends Stack { public void pop(int n) { addAction(Actions.run(() -> { if (!hasChildren() || n == 0) { return; } SnapshotArray<Actor> children = getChildren(); int size = children.size; children.removeRange(Math.max(0, size - n), size - 1); if (size - n > 0) { getStage().setKeyboardFocus(children.peek()); } })); }  void replace(Actor screen); void push(Actor screen); void pop(int n); @Override void act(float deltaTime);  }### Answer:
@Test public void testPopNoChildren() throws Exception { latch = new CountDownLatch(1); app.postRunnable(() -> { actor.pop(1); latch.countDown(); }); assertThat(latch.await(5, TimeUnit.SECONDS)).isTrue(); Thread.sleep(500); assertThat(actor.hasChildren()).isFalse(); }