trueskill-tt/tests/ingestion_shape.rs

//! Malformed events must be rejected at the ingestion boundary.
//!
//! Every case here was reachable from safe public API in a release build. Two
//! of them are the two shapes this crate's defects keep taking: a panic from
//! deep inside inference, and a finite, plausible-looking posterior computed
//! from an event that should never have been accepted.
//!
//! `InferenceError::NotEnoughTeams` and `EmptyTeam` already existed when these
//! were found — they were checked on the prediction paths and nowhere else, so
//! ingestion could still manufacture the states they describe.

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

type Ev = Event<i64, &'static str>;

fn history() -> History {
    History::builder().score_sigma(1.0).build()
}

fn teams(names: &[&[&'static str]]) -> smallvec::SmallVec<[Team<&'static str>; 4]> {
    names
        .iter()
        .map(|team| Team::with_members(team.iter().map(|k| Member::new(*k))))
        .collect()
}

/// The regression this file exists for: `run_chain` builds one diff link per
/// adjacent pair of teams, so a one-team event left it indexing `links[1..]`
/// on an empty vector and panicked — in release, from `History::add_events`.
#[test]
fn a_one_team_event_is_an_error_not_a_panic() {
    let mut h = history();
    let err = h
        .add_events(vec![Ev {
            time: 1,
            teams: teams(&[&["a"]]),
            outcome: Outcome::winner(0, 1),
        }])
        .unwrap_err();
    assert!(
        matches!(err, InferenceError::NotEnoughTeams { got: 1, .. }),
        "{err:?}"
    );
}

#[test]
fn a_zero_team_event_is_an_error() {
    let mut h = history();
    let err = h
        .add_events(vec![Ev {
            time: 1,
            teams: smallvec![],
            outcome: Outcome::ranking([]),
        }])
        .unwrap_err();
    assert!(
        matches!(err, InferenceError::NotEnoughTeams { got: 0, .. }),
        "{err:?}"
    );
}

/// The quiet half. An empty team contributes no performance, so before this
/// was rejected the event converged and handed back a finite posterior for its
/// opponent — a plausible constant computed from nothing.
#[test]
fn an_empty_team_is_an_error_rather_than_a_free_win() {
    let mut h = history();
    let err = h
        .add_events(vec![Ev {
            time: 1,
            teams: teams(&[&[], &["b"]]),
            outcome: Outcome::winner(0, 2),
        }])
        .unwrap_err();
    assert!(
        matches!(err, InferenceError::EmptyTeam { team: 0, .. }),
        "{err:?}"
    );
    // Nothing was recorded, so the history is still empty.
    assert!(h.current_skill(&"b").is_none());
}

#[test]
fn an_empty_team_is_reported_by_position() {
    let mut h = history();
    let err = h
        .add_events(vec![Ev {
            time: 1,
            teams: teams(&[&["a"], &[]]),
            outcome: Outcome::winner(0, 2),
        }])
        .unwrap_err();
    assert!(
        matches!(err, InferenceError::EmptyTeam { team: 1, .. }),
        "{err:?}"
    );
}

/// A NaN score used to ingest cleanly. `converge` reported `NonFiniteResult`,
/// but a caller who read `current_skill` first was handed `tau: NaN` with
/// nothing to say so.
#[test]
fn a_non_finite_score_is_rejected_at_ingestion() {
    for bad in [f64::NAN, f64::INFINITY, f64::NEG_INFINITY] {
        let mut h = history();
        let err = h
            .add_events(vec![Ev {
                time: 1,
                teams: teams(&[&["a"], &["b"]]),
                outcome: Outcome::scores([bad, 0.0]),
            }])
            .unwrap_err();
        assert!(
            matches!(
                err,
                InferenceError::InvalidParameter {
                    parameter: trueskill_tt::Parameter::Score,
                    ..
                }
            ),
            "{bad}: {err:?}"
        );
        assert!(h.current_skill(&"a").is_none(), "{bad} was recorded anyway");
    }
}

/// A non-finite weight behaved exactly as `0.0` — the member contributed
/// nothing — while `converge` reported `converged: true` after one iteration
/// with a step of `(0.0, 0.0)`. So a NaN arriving from a division or a parse
/// was indistinguishable from a deliberate zero, and looked like a clean fit.
#[test]
fn a_non_finite_weight_is_rejected_at_ingestion() {
    for bad in [f64::NAN, f64::INFINITY, f64::NEG_INFINITY] {
        let mut h = history();
        let err = h
            .event(1)
            .team(["a"])
            .weights([bad])
            .team(["b"])
            .winner(0)
            .commit()
            .unwrap_err();
        assert!(
            matches!(
                err,
                InferenceError::InvalidParameter {
                    parameter: trueskill_tt::Parameter::Weight,
                    ..
                }
            ),
            "{bad}: {err:?}"
        );
        assert!(h.current_skill(&"a").is_none(), "{bad} reached the history");
    }
}

/// Zero and negative weights are expressible choices about how much a member
/// contributes, not malformed input, and `tests/degenerate_inputs.rs` pins
/// their behaviour deliberately. Rejecting non-finite values must not catch
/// them too.
#[test]
fn zero_and_negative_weights_still_ingest() {
    for w in [0.0, -1.0, 0.5] {
        let mut h = history();
        h.event(1)
            .team(["a"])
            .weights([w])
            .team(["b"])
            .winner(0)
            .commit()
            .unwrap_or_else(|e| panic!("weight {w} should ingest: {e:?}"));
        assert!(h.current_skill(&"a").is_some(), "weight {w}");
    }
}

/// The fluent builder routes through the same chokepoint, so it inherits the
/// checks rather than needing its own.
#[test]
fn the_event_builder_inherits_the_shape_checks() {
    let mut h = history();
    let err = h.event(1).team(["a"]).winner(0).commit().unwrap_err();
    assert!(
        matches!(err, InferenceError::NotEnoughTeams { got: 1, .. }),
        "{err:?}"
    );
}

/// A well-formed event is untouched by any of this.
#[test]
fn a_well_formed_event_still_ingests() {
    let mut h = history();
    h.add_events(vec![Ev {
        time: 1,
        teams: teams(&[&["a"], &["b"]]),
        outcome: Outcome::scores([3.0, 1.0]),
    }])
    .unwrap();
    assert!(h.converge().unwrap().converged);
    assert!(h.current_skill(&"a").unwrap().mu() > h.current_skill(&"b").unwrap().mu());
}