public void testLongRepresenter() {
DumperOptions options = new DumperOptions();
options.setDefaultScalarStyle(DumperOptions.ScalarStyle.DOUBLE_QUOTED);
Representer repr = new Representer();
repr.addClassTag(Long.class, new Tag("!!java.lang.Long"));
Yaml yaml = new Yaml(repr, options);
Foo foo = new Foo();
String output = yaml.dump(foo);
// System.out.println(output);