provider.setNamespacePrefixes(
Collections.singletonMap("http://tags", "prefix"));
TagVO2 tag = new TagVO2("a", "b");
List<TagVO2> tags = Collections.singletonList(tag);
ByteArrayOutputStream bos = new ByteArrayOutputStream();
provider.writeTo(tags, List.class, new ParameterizedCollectionType(TagVO2.class),
new Annotation[0], MediaType.TEXT_XML_TYPE, new MetadataMap<String, Object>(), bos);
assertTrue(bos.toString().contains("prefix:thetag"));
assertFalse(bos.toString().contains("ns1:thetag"));
}