I have been taking various training tests and the answer almost always involves some sort of forcing move. Clearly attacking a king will always force a response but when another piece is involved (whether it be major or minor) an attack does not need to be forcing. Are there rules of thumb to help identify forces in these cases? I tend to look for mates, royal forks followed by forks and then winning exchanges. Where I stumble is if a test involves a forcing attack that leads to mate. I always just assume I would sacrifice the piece to stay alive.