public void popNode() {
    current.finishSpecifying();
    unexpandedInputs.remove(current);
    current = current.getEnclosingNode();
    checkState(current != null, "Can't pop the root node of a TransformHierarchy");
  }
@Test
  public void pushWithoutPushFails() {
    thrown.expect(IllegalStateException.class);
    hierarchy.popNode();
  }