@Test
public void testRetrieveUserFromEngine() {

    Optional<User> result = engineManager.retrieveUser(ERROR, "user");
    verify(engine, times(0)).retrieveUser("user");
    assertFalse(result.isPresent());
    result = engineManager.retrieveUser(engine.getEngineName(), "user");
    verify(engine).retrieveUser("user");
    assertTrue(result.isPresent());
    assertEquals(user, result.get());
}