@Test
public void populatesUsersToLikes() {

    String id = "someId";
    Like like = mock(Like.class);
    List<Like> likes = Arrays.asList(like);
    Map<String, User> userMap = new HashMap<>();
    User user = mock(User.class);
    userMap.put(id, user);
    when(like.getUserId()).thenReturn(id);
    LikesFeed feed = new LikesFeed();
    feed.likes = likes;
    feed.users = userMap;
    feed.posts = new HashMap<>();
    feed.flatten();
    verify(like).setUser(user);
}