@Override
  public List<String> getGroups(String userName) throws IOException {
    return new ArrayList(getUnixGroups(userName));
  }
@Test
  public void testGetNumericGroupsResolvable() throws Exception {
    TestNumericGroupResolvable mapping = new TestNumericGroupResolvable();

    List<String> groups = mapping.getGroups("user");
    assertTrue(groups.size() == 3);
    assertTrue(groups.contains("23"));
    assertTrue(groups.contains("groupname"));
    assertTrue(groups.contains("zzz"));
  }