void doSubmit(final Runnable action) {
    CONTINUATION.get().submit(action);
  }
@Test
  public void testRecursiveOrderWithException() {
    final Continuations CONT = new Continuations();
    final StringBuilder result = new StringBuilder();
    try {
      CONT.doSubmit(() -> {
        result.append("BEGIN{");
        recursivePostOrderWithException(CONT, result, "root", 0);
      });
      CONT.doSubmit(() -> {
        result.append("}END");
      });
      fail("should have thrown exception");
    } catch (Exception e) {
      assertEquals(e.getMessage(), "nested");
    }
    assertEquals(result.toString(), "BEGIN{[done(rootLL:2)][done(rootLR:2)][done(rootL:1)][done(rootRL:2)]");
  }