child.setParentGroup(parent);
HashSet<ContentItemGroupDTO> childGroups = newInstance(HashSet.class);
childGroups.add(child);
parent.setChildGroups(childGroups);
ContentItemGroup result = mapper.map(parent, ContentItemGroupDefault.class);
assertNotNull(result);
ContentItemGroup childResult = (ContentItemGroup) result.getChildGroups().iterator().next();
assertEquals(result, childResult.getParentGroup());
assertEquals("A", result.getId());
assertEquals("B", childResult.getId());
}