@Test
public void testAddUser() {

    configureWithInitialUsers();
    final Set<User> users = userGroupProvider.getUsers();
    assertEquals(0, users.size());
    final User user1 = new User.Builder()
            .identifier(UUID.randomUUID().toString())
            .identity("user1")
            .build();
    final User createdUser1 = userGroupProvider.addUser(user1);
    assertNotNull(createdUser1);
    final Set<User> usersAfterCreate = userGroupProvider.getUsers();
    assertEquals(1, usersAfterCreate.size());
    final User retrievedUser1 = usersAfterCreate.stream().findFirst().get();
    assertEquals(user1.getIdentifier(), retrievedUser1.getIdentifier());
    assertEquals(user1.getIdentity(), retrievedUser1.getIdentity());
}