@Test
public void testGetUsers() {

    // Setup:
    Set<String> expectedUsernames = Stream.of("admin", username).collect(Collectors.toSet());
    Set<User> users = engine.getUsers();
    assertEquals(expectedUsernames.size(), users.size());
    users.forEach(user -> {
        Optional<Literal> optUsername = user.getUsername();
        assertTrue(optUsername.isPresent());
        assertTrue(expectedUsernames.contains(optUsername.get().stringValue()));
    });
}