void doSubmit(final Runnable action) {
    CONTINUATION.get().submit(action);
  }
@Test
  public void testRecursiveOrder() {
    final Continuations CONT = new Continuations();
    final StringBuilder result = new StringBuilder();
    CONT.doSubmit(() -> {
      result.append("BEGIN{");
      recursivePostOrder(CONT, result, "root", 0);
    });
    CONT.doSubmit(() -> {
      result.append("}END");
    });
    assertEquals(result.toString(),
        "BEGIN{[done(rootLL:2)][done(rootLR:2)][done(rootL:1)][done(rootRL:2)][done(rootRR:2)][done(rootR:1)][done(root:0)]}END");
  }