Function kept 

pub fn kept(
    game: &dyn GameTools,
    root: &Path,
    input: &PlaytestInput,
) -> Answer<Vec<PlaytestOutput>>

playtest, each stage’s run kept in the history under root (unless no_history) and compared with the last one kept there: each entrant’s was and the stage’s previous. A history that can’t be written fails the answer, naming the file.