### Question:
ExternalGroupsRepository implements Repository { @Override public CheckpointCloseableIterable<IdentityUser> listUsers(byte[] checkpoint) throws IOException { throw new UnsupportedOperationException("Method not supported."); } ExternalGroupsRepository(); @VisibleForTesting  ExternalGroupsRepository(GroupsReader groupsReader); @Override void init(RepositoryContext context); @Override CheckpointCloseableIterable<IdentityGroup> listGroups(byte[] checkpoint); @Override CheckpointCloseableIterable<IdentityUser> listUsers(byte[] checkpoint); @Override void close();  }### Answer:
@Test public void listUsers_throwsException() throws Exception { ExternalGroupsRepository groupsRepository = new ExternalGroupsRepository(); thrown.expect(UnsupportedOperationException.class); groupsRepository.listUsers(null); }