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

    List<String> groups = mapping.getGroups("foobarusernotexist");
    assertTrue(groups.isEmpty());
  }