trueskill-tt/tests/validation.rs

//! Input validation must hold in **release**, where `debug_assert!` is gone.
//!
//! The engine guards itself with `debug_assert!`, which documents invariants
//! but vanishes in the profile users actually ship. Anything reachable from the
//! public API has to be rejected with an `InferenceError` instead, at the
//! boundary, rather than becoming NaN or an out-of-bounds panic deep inside
//! `run_chain`.
//!
//! `GameOptions` and `ConvergenceOptions` both have public fields, so the
//! eager asserts on `HistoryBuilder` do not cover the `Game` constructors —
//! a caller can build the options struct directly.

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

type R = Rating<i64, ConstantDrift>;

fn rating() -> R {
    R::new(
        Gaussian::from_ms(25.0, 25.0 / 3.0),
        25.0 / 6.0,
        ConstantDrift(0.0),
    )
}

fn options_with_alpha(alpha: f64) -> GameOptions {
    GameOptions {
        convergence: ConvergenceOptions {
            alpha,
            ..ConvergenceOptions::default()
        },
        ..GameOptions::default()
    }
}

/// `alpha == 0.0` leaves every EP update unapplied, so inference silently
/// returns the priors — the worst possible failure, since the output looks
/// entirely reasonable.
#[test]
fn ranked_rejects_a_zero_damping_factor() {
    let (a, b) = (rating(), rating());
    let err = Game::<i64, _>::ranked(
        &[&[a], &[b]],
        Outcome::winner(0, 2),
        &options_with_alpha(0.0),
    )
    .expect_err("alpha = 0 must be rejected");
    assert!(
        matches!(err, InferenceError::InvalidParameter { name: "alpha", .. }),
        "got {err:?}"
    );
}

#[test]
fn ranked_rejects_an_out_of_range_damping_factor() {
    let (a, b) = (rating(), rating());
    for alpha in [-0.5, 1.5, f64::NAN] {
        let err = Game::<i64, _>::ranked(
            &[&[a], &[b]],
            Outcome::winner(0, 2),
            &options_with_alpha(alpha),
        )
        .expect_err("alpha out of (0, 1] must be rejected");
        assert!(
            matches!(err, InferenceError::InvalidParameter { name: "alpha", .. }),
            "alpha={alpha}: got {err:?}"
        );
    }
}

#[test]
fn scored_rejects_a_bad_damping_factor() {
    let (a, b) = (rating(), rating());
    let err = Game::<i64, _>::scored(
        &[&[a], &[b]],
        Outcome::scores([21.0, 9.0]),
        &options_with_alpha(0.0),
    )
    .expect_err("alpha = 0 must be rejected");
    assert!(
        matches!(err, InferenceError::InvalidParameter { name: "alpha", .. }),
        "got {err:?}"
    );
}

/// Already covered by `Game::ranked`, asserted here so the release-mode
/// guarantee is stated in one place.
#[test]
fn ranked_rejects_an_out_of_range_draw_probability() {
    let (a, b) = (rating(), rating());
    for p_draw in [-0.5, 1.0, 1.5] {
        let options = GameOptions {
            p_draw,
            ..GameOptions::default()
        };
        assert!(
            Game::<i64, _>::ranked(&[&[a], &[b]], Outcome::winner(0, 2), &options).is_err(),
            "p_draw={p_draw} must be rejected"
        );
    }
}

#[test]
fn scored_rejects_a_non_positive_noise() {
    let (a, b) = (rating(), rating());
    for score_sigma in [0.0, -1.0, f64::NAN] {
        let options = GameOptions {
            score_sigma,
            ..GameOptions::default()
        };
        assert!(
            Game::<i64, _>::scored(&[&[a], &[b]], Outcome::scores([21.0, 9.0]), &options).is_err(),
            "score_sigma={score_sigma} must be rejected"
        );
    }
}

/// A tie with no draw probability makes the truncation margin zero and the
/// two-sided update evaluate 0/0. Ingestion must refuse it.
#[test]
fn ingestion_rejects_a_tie_without_a_draw_probability() {
    let mut h = History::builder().p_draw(0.0).build();
    let err = h
        .add_events(vec![Event {
            time: 0,
            teams: smallvec![
                Team::with_members([Member::new("a")]),
                Team::with_members([Member::new("b")]),
            ],
            outcome: Outcome::draw(2),
        }])
        .expect_err("a tie with p_draw = 0 must be rejected");
    assert!(
        matches!(err, InferenceError::TieWithoutDrawProbability { .. }),
        "got {err:?}"
    );
}

/// `Outcome::scores_with_sigma` documents that a non-positive sigma is
/// accepted at construction and rejected at ingestion.
#[test]
fn ingestion_rejects_a_non_positive_per_event_score_sigma() {
    for sigma in [0.0, -1.0, f64::NAN] {
        let mut h = History::builder().build();
        let err = h
            .add_events(vec![Event {
                time: 0,
                teams: smallvec![
                    Team::with_members([Member::new("a")]),
                    Team::with_members([Member::new("b")]),
                ],
                outcome: Outcome::scores_with_sigma([21.0, 9.0], sigma),
            }])
            .expect_err("a non-positive per-event sigma must be rejected");
        assert!(
            matches!(err, InferenceError::InvalidParameter { .. }),
            "sigma={sigma}: got {err:?}"
        );
    }
}

/// Per-team weights must match that team's membership. The top-level length
/// checks in ingestion do not cover the inner dimension.
#[test]
fn ingestion_rejects_weights_that_do_not_match_their_team() {
    let mut h = History::builder().build();
    let mut team = Team::with_members([Member::new("a"), Member::new("b")]);
    team.members[0].weight = 1.0;

    let err = h
        .event(0)
        .team(["a", "b"])
        .team(["c"])
        // Three weights for a two-member team.
        .weights([1.0, 1.0, 1.0])
        .winner(0)
        .commit()
        .expect_err("a weight/member length mismatch must be rejected");
    assert!(
        matches!(err, InferenceError::MismatchedShape { .. }),
        "got {err:?}"
    );
}

/// `mu`, `sigma` and `beta` were the last unvalidated setters on
/// `HistoryBuilder`, next to `p_draw`, `score_sigma` and `convergence`, which
/// all assert eagerly.
///
/// Two of the rejected values are the quiet kind. A negative `sigma` or `beta`
/// enters inference only as its square, so it produced bit-identical results
/// to the positive value — the sign was dropped without comment.
mod builder_parameters {
    use trueskill_tt::History;

    #[test]
    #[should_panic(expected = "mu must be finite")]
    fn a_non_finite_mu_is_rejected() {
        let _ = History::builder().mu(f64::NAN);
    }

    #[test]
    #[should_panic(expected = "sigma must be finite and positive")]
    fn a_zero_sigma_is_rejected() {
        let _ = History::builder().sigma(0.0);
    }

    #[test]
    #[should_panic(expected = "sigma must be finite and positive")]
    fn a_negative_sigma_is_rejected() {
        let _ = History::builder().sigma(-8.33);
    }

    #[test]
    #[should_panic(expected = "sigma must be finite and positive")]
    fn an_infinite_sigma_is_rejected() {
        let _ = History::builder().sigma(f64::INFINITY);
    }

    #[test]
    #[should_panic(expected = "beta must be finite and non-negative")]
    fn a_negative_beta_is_rejected() {
        let _ = History::builder().beta(-4.17);
    }

    #[test]
    #[should_panic(expected = "beta must be finite and non-negative")]
    fn a_non_finite_beta_is_rejected() {
        let _ = History::builder().beta(f64::NAN);
    }

    /// Zero beta is deliberately allowed: performance is then exactly skill.
    /// It has to reach a different fit than a positive beta, or "allowed"
    /// would just mean "not checked".
    #[test]
    fn a_zero_beta_is_allowed_and_changes_the_fit() {
        let fit = |beta: f64| {
            let mut h = History::builder()
                .mu(25.0)
                .sigma(25.0 / 3.0)
                .beta(beta)
                .build();
            h.record_winner(&"a", &"b", 1).unwrap();
            let _ = h.converge().unwrap();
            h.current_skill(&"a").unwrap()
        };
        let zero = fit(0.0);
        let positive = fit(25.0 / 6.0);
        assert!(zero.pi().is_finite() && zero.pi() > 0.0);
        assert!(
            (zero.pi() - positive.pi()).abs() > 1e-6,
            "zero beta must not merely be ignored: {zero:?} vs {positive:?}"
        );
    }
}