assertThat(iterationOrder(ADAPTER.postOrderTraversal(h))).isEqualTo("abcdefgh");
  }

  public void testBreadthOrder() {
    assertThat(iterationOrder(ADAPTER.breadthFirstTraversal(h))).isEqualTo("hdegabcf");
  }

  public void testUsing() {
    assertThat(iterationOrder(ADAPTER_USING_USING.preOrderTraversal(h))).isEqualTo("hdabcegf");
  }

  @J2ktIncompatible
  @GwtIncompatible // NullPointerTester