trueskill-tt/tests/observer.rs

//! `Observer` callbacks must actually fire.
//!
//! `on_slice_processed` (formerly `on_batch_processed`) was declared on the
//! trait and never called from anywhere, so implementors wired up a callback
//! that could not run. These tests exist so that cannot silently recur.

use std::sync::{Arc, Mutex};

use trueskill_tt::{History, Observer};

/// Plain fields. `Arc<O>` implements `Observer`, so the caller shares the
/// observer itself rather than wrapping each field in its own `Arc`.
#[derive(Default)]
struct Recorder {
    iterations: Mutex<Vec<usize>>,
    slices: Mutex<Vec<(i64, usize, usize)>>,
    converged: Mutex<Vec<(usize, bool)>>,
}

impl Observer<i64> for Recorder {
    fn on_iteration_end(&self, iter: usize, _max_step: (f64, f64)) {
        self.iterations.lock().unwrap().push(iter);
    }

    fn on_slice_processed(&self, time: &i64, slice_idx: usize, n_events: usize) {
        self.slices
            .lock()
            .unwrap()
            .push((*time, slice_idx, n_events));
    }

    fn on_converged(&self, iters: usize, _final_step: (f64, f64), converged: bool) {
        self.converged.lock().unwrap().push((iters, converged));
    }
}

#[test]
fn every_observer_callback_fires() {
    let recorder = Arc::new(Recorder::default());
    let mut h = History::builder().observer(Arc::clone(&recorder)).build();

    h.record_winner(&"a", &"b", 1).unwrap();
    h.record_winner(&"b", &"c", 2).unwrap();
    h.record_winner(&"c", &"a", 3).unwrap();
    h.converge().unwrap();

    assert!(
        !recorder.iterations.lock().unwrap().is_empty(),
        "on_iteration_end never fired"
    );
    assert!(
        !recorder.converged.lock().unwrap().is_empty(),
        "on_converged never fired"
    );
    assert!(
        !recorder.slices.lock().unwrap().is_empty(),
        "on_slice_processed never fired — the defect this test exists for"
    );
}

#[test]
fn slice_callbacks_report_the_slice_they_swept() {
    let recorder = Arc::new(Recorder::default());
    let mut h = History::builder().observer(Arc::clone(&recorder)).build();

    h.record_winner(&"a", &"b", 10).unwrap();
    h.record_winner(&"a", &"b", 20).unwrap();
    h.converge().unwrap();

    let slices = recorder.slices.lock().unwrap();

    // Only the times actually in the history, and each with its own events.
    for &(time, idx, events) in slices.iter() {
        assert!(time == 10 || time == 20, "unexpected slice time {time}");
        assert!(idx < 2, "slice index {idx} out of range");
        assert_eq!(events, 1, "each slice holds exactly one event");
    }

    // Both slices must be reported, not just one end of the sweep.
    assert!(
        slices.iter().any(|&(t, ..)| t == 10),
        "slice 10 never reported"
    );
    assert!(
        slices.iter().any(|&(t, ..)| t == 20),
        "slice 20 never reported"
    );
}

#[test]
fn a_single_slice_history_still_reports_its_sweep() {
    let recorder = Arc::new(Recorder::default());
    let mut h = History::builder().observer(Arc::clone(&recorder)).build();

    h.record_winner(&"a", &"b", 1).unwrap();
    h.converge().unwrap();

    let slices = recorder.slices.lock().unwrap();
    assert!(
        !slices.is_empty(),
        "the single-slice path must report its sweep too"
    );
    assert!(slices.iter().all(|&(t, idx, _)| t == 1 && idx == 0));
}

/// The gap #40 closed: without `impl Observer for Arc<O>`, an observer that
/// accumulates anything had to wrap every field in its own `Arc` and derive
/// `Clone`, because `History` consumes the observer and never hands it back.
#[test]
fn a_shared_observer_reaches_the_callers_handle() {
    let recorder = Arc::new(Recorder::default());
    let mut h = History::builder().observer(Arc::clone(&recorder)).build();

    h.record_winner(&"a", &"b", 1).unwrap();
    h.converge().unwrap();

    assert!(!recorder.iterations.lock().unwrap().is_empty());
    assert!(!recorder.slices.lock().unwrap().is_empty());
    assert!(!recorder.converged.lock().unwrap().is_empty());
}

/// `?Sized` on the blanket impls means the observer can be chosen at runtime.
#[test]
fn a_trait_object_observer_works() {
    let boxed: Box<dyn Observer<i64>> = Box::new(Recorder::default());
    let mut h = History::builder().observer(boxed).build();
    h.record_winner(&"a", &"b", 1).unwrap();
    h.converge().unwrap();

    let shared: Arc<dyn Observer<i64>> = Arc::new(Recorder::default());
    let mut h = History::builder().observer(Arc::clone(&shared)).build();
    h.record_winner(&"a", &"b", 1).unwrap();
    h.converge().unwrap();
}

/// A non-shared observer can be reclaimed after convergence instead.
#[test]
fn into_observer_returns_the_accumulated_state() {
    let mut h = History::builder().observer(Recorder::default()).build();
    h.record_winner(&"a", &"b", 1).unwrap();
    h.converge().unwrap();

    // Readable in place...
    assert!(!h.observer().iterations.lock().unwrap().is_empty());

    // ...and reclaimable by value.
    let recorder = h.into_observer();
    assert!(!recorder.slices.lock().unwrap().is_empty());
}

/// Borrowing works too, for an observer that outlives the history.
#[test]
fn a_borrowed_observer_works() {
    let recorder = Recorder::default();
    {
        let mut h = History::builder().observer(&recorder).build();
        h.record_winner(&"a", &"b", 1).unwrap();
        h.converge().unwrap();
    }
    assert!(!recorder.iterations.lock().unwrap().is_empty());
}