trueskill-tt/tests/competitor_config.rs

//! `Member::with_prior` / `with_drift_scale` — competitor configuration.
//!
//! Both were previously consumed only on the branch that *creates* a
//! competitor, so configuration supplied for a key the history already knew was
//! dropped with no error. `with_prior` had no coverage in this directory at
//! all, which is how that survived.

use smallvec::smallvec;
use trueskill_tt::{
    ConvergenceOptions, Event, Gaussian, History, InferenceError, Member, Outcome, Team,
};

const CONVERGENCE: ConvergenceOptions = ConvergenceOptions {
    max_iter: 2_000,
    epsilon: 1e-12,
    alpha: 1.0,
};

fn history() -> History {
    History::builder()
        .mu(25.0)
        .sigma(25.0 / 3.0)
        .beta(25.0 / 6.0)
        .p_draw(0.0)
        .convergence(CONVERGENCE)
        .build()
}

/// One event, optionally configuring `a`.
fn bout(
    a: &'static str,
    b: &'static str,
    time: i64,
    prior: Option<Gaussian>,
    scale: Option<f64>,
) -> Event<i64, &'static str> {
    let mut member = Member::new(a);
    if let Some(p) = prior {
        member = member.with_prior(p);
    }
    if let Some(s) = scale {
        member = member.with_drift_scale(s);
    }

    Event {
        time,
        teams: smallvec![
            Team::with_members([member]),
            Team::with_members([Member::new(b)]),
        ],
        outcome: Outcome::winner(0, 2),
    }
}

fn skill_of(h: &History, key: &str) -> Gaussian {
    h.current_skill(&key).expect("key in history")
}

/// Baseline: the mechanism works at all on a competitor's first appearance.
#[test]
fn a_prior_applies_to_a_new_competitor() {
    let seeded = Gaussian::from_ms(40.0, 1.0);

    let mut with = history();
    with.add_events(vec![bout("a", "b", 0, Some(seeded), None)])
        .unwrap();
    let _ = with.converge().unwrap();

    let mut without = history();
    without
        .add_events(vec![bout("a", "b", 0, None, None)])
        .unwrap();
    let _ = without.converge().unwrap();

    assert!(
        (skill_of(&with, "a").mu() - skill_of(&without, "a").mu()).abs() > 1.0,
        "a seeded prior should move the fit"
    );
}

/// The defect in #10: a prior supplied for a competitor the history already
/// knows was silently discarded, and the caller got output computed from the
/// default prior with no indication anything had been dropped.
#[test]
fn a_prior_applies_to_a_competitor_the_history_already_knows() {
    let seeded = Gaussian::from_ms(40.0, 1.0);

    let mut late = history();
    late.add_events(vec![bout("a", "b", 0, None, None)])
        .unwrap();
    // "a" now exists. Configuring it here used to do nothing whatsoever.
    late.add_events(vec![bout("a", "b", 1, Some(seeded), None)])
        .unwrap();
    let _ = late.converge().unwrap();

    let mut never = history();
    never
        .add_events(vec![
            bout("a", "b", 0, None, None),
            bout("a", "b", 1, None, None),
        ])
        .unwrap();
    let _ = never.converge().unwrap();

    assert!(
        (skill_of(&late, "a").mu() - skill_of(&never, "a").mu()).abs() > 1.0,
        "a late prior must not be silently dropped: {} vs {}",
        skill_of(&late, "a").mu(),
        skill_of(&never, "a").mu()
    );
}

/// Configuration is competitor-scoped, not event-scoped, and `converge` refits
/// from competitor state — so seeding late reaches the same fit as seeding from
/// the start. This is the documented scope, asserted rather than assumed.
#[test]
fn a_prior_is_whole_history_scoped_not_per_event() {
    let seeded = Gaussian::from_ms(40.0, 1.0);

    let mut late = history();
    late.add_events(vec![bout("a", "b", 0, None, None)])
        .unwrap();
    late.add_events(vec![bout("a", "b", 1, Some(seeded), None)])
        .unwrap();
    let _ = late.converge().unwrap();

    let mut early = history();
    early
        .add_events(vec![
            bout("a", "b", 0, Some(seeded), None),
            bout("a", "b", 1, Some(seeded), None),
        ])
        .unwrap();
    let _ = early.converge().unwrap();

    let (l, e) = (skill_of(&late, "a"), skill_of(&early, "a"));
    assert!(
        (l.mu() - e.mu()).abs() < 1e-9 && (l.sigma() - e.sigma()).abs() < 1e-9,
        "late seeding should refit the whole history: {l:?} vs {e:?}"
    );
}

#[test]
fn repeating_the_same_prior_is_inert() {
    let seeded = Gaussian::from_ms(40.0, 1.0);

    let mut once = history();
    once.add_events(vec![
        bout("a", "b", 0, Some(seeded), None),
        bout("a", "b", 1, None, None),
    ])
    .unwrap();
    let _ = once.converge().unwrap();

    let mut every_time = history();
    every_time
        .add_events(vec![
            bout("a", "b", 0, Some(seeded), None),
            bout("a", "b", 1, Some(seeded), None),
        ])
        .unwrap();
    let _ = every_time.converge().unwrap();

    let (o, e) = (skill_of(&once, "a"), skill_of(&every_time, "a"));
    assert!(
        (o.mu() - e.mu()).abs() < 1e-12 && (o.sigma() - e.sigma()).abs() < 1e-12,
        "declaring the same prior repeatedly changed the fit: {o:?} vs {e:?}"
    );
}

/// Events within a batch have no order, so two different values for one
/// competitor have no well-defined winner. Rejecting is what keeps the answer
/// independent of iteration order.
#[test]
fn a_batch_declaring_two_different_priors_is_rejected() {
    let mut h = history();
    let err = h
        .add_events(vec![
            bout("a", "b", 0, Some(Gaussian::from_ms(40.0, 1.0)), None),
            bout("a", "b", 1, Some(Gaussian::from_ms(10.0, 1.0)), None),
        ])
        .expect_err("two different priors for one competitor in one batch");

    assert!(
        matches!(
            err,
            InferenceError::ConflictingCompetitorConfig { field: "prior", .. }
        ),
        "got {err:?}"
    );
}

/// A member setting only `drift_scale` must not also assert the default prior,
/// or it would silently undo a prior seeded earlier. This is why the collected
/// configuration tracks each field separately rather than a merged `Rating`.
#[test]
fn setting_one_field_late_leaves_the_other_alone() {
    let seeded = Gaussian::from_ms(40.0, 1.0);

    let mut h = history();
    h.add_events(vec![bout("a", "b", 0, Some(seeded), None)])
        .unwrap();
    // Only the scale this time — the prior above must survive.
    h.add_events(vec![bout("a", "b", 1, None, Some(0.5))])
        .unwrap();
    let _ = h.converge().unwrap();

    let mut both_upfront = history();
    both_upfront
        .add_events(vec![
            bout("a", "b", 0, Some(seeded), Some(0.5)),
            bout("a", "b", 1, None, None),
        ])
        .unwrap();
    let _ = both_upfront.converge().unwrap();

    let (a, b) = (skill_of(&h, "a"), skill_of(&both_upfront, "a"));
    assert!(
        (a.mu() - b.mu()).abs() < 1e-9 && (a.sigma() - b.sigma()).abs() < 1e-9,
        "setting drift_scale late clobbered the earlier prior: {a:?} vs {b:?}"
    );
}