public static void main(String[] args) {
    var root = new NodeImpl("1",
        new NodeImpl("11",
            new NodeImpl("111", NullNode.getInstance(), NullNode.getInstance()),
            NullNode.getInstance()
        ),
        new NodeImpl("12",
            NullNode.getInstance(),
            new NodeImpl("122", NullNode.getInstance(), NullNode.getInstance())
        )
    );

    root.walk();
  }
@Test
  void shouldExecuteApplicationWithoutException() {
    assertDoesNotThrow(() -> App.main(new String[]{}));
  }