trueskill-tt/tests/key_ergonomics.rs

//! The realistic program: keys arrive owned, queries are written with literals.
//!
//! Every prediction and joint query used to take `&[&[&K]]`, which at
//! `K = String` made a string literal *impossible* — the shape required three
//! levels of temporaries that all had to outlive the call. They are generic
//! over the borrowed key now, so one spelling works at both key types.
//!
//! Both key types are exercised in every test, because the point is that the
//! spelling is the same.

use trueskill_tt::{ConstantDrift, History, NullObserver};

type Owned = History<i64, ConstantDrift, NullObserver, String>;
type Borrowed = History<i64, ConstantDrift, NullObserver, &'static str>;

fn owned() -> Owned {
    let mut h: Owned = History::builder().key_type::<String>().build();
    for t in 1..=4 {
        h.record_winner(&"alice".to_string(), &"bob".to_string(), t)
            .expect("ingests");
    }
    h.converge().expect("converges");
    h
}

fn borrowed() -> Borrowed {
    let mut h = History::default();
    for t in 1..=4 {
        h.record_winner(&"alice", &"bob", t).expect("ingests");
    }
    h.converge().expect("converges");
    h
}

#[test]
fn predictions_take_literals_at_either_key_type() {
    let teams: &[&[&str]] = &[&["alice"], &["bob"]];

    let a = owned()
        .predict_win_probabilities(teams)
        .expect("K = String");
    let b = borrowed()
        .predict_win_probabilities(teams)
        .expect("K = &'static str");

    assert_eq!(a, b, "the same fit through the same spelling");
    assert!(a[0] > a[1], "alice won every game");
}

#[test]
fn every_team_shaped_query_accepts_the_same_slice() {
    let h = owned();
    let teams: &[&[&str]] = &[&["alice"], &["bob"]];

    h.quality(teams).expect("quality");
    let _ = h.predict_outcome(teams).expect("outcome");
    h.predict_ranking(teams, &[0, 1]).expect("ranking");
    h.expected_information_gain(teams)
        .expect("information gain");
}

#[test]
fn linear_combinations_take_bare_keys() {
    // `&[(&K, f64)]` at `K = String` meant `&[(&String, f64)]` — no literals.
    let h = owned();
    let terms: &[(&str, f64)] = &[("alice", 1.0), ("bob", -1.0)];

    // Ranked history, so the joint is unavailable — but the *call* compiles,
    // which is what this pins. The error proves it reached the joint check
    // rather than failing to resolve a key.
    let err = h
        .posterior_of(terms)
        .expect_err("ranked history has no joint");
    assert!(
        format!("{err}").contains("ranked"),
        "expected the joint-unavailable path, got {err}"
    );
}

/// `lookup` is gone with `Index` (#73); the accessors that answer the same
/// question all take a borrowed key.
#[test]
fn membership_queries_accept_a_borrowed_key() {
    let h = owned();
    assert!(h.current_skill("alice").is_some());
    assert!(h.rating("alice").is_some());
    assert!(h.learning_curve("alice").is_some());

    assert!(h.current_skill("nobody").is_none());
    assert!(h.rating("nobody").is_none());
    assert!(h.learning_curve("nobody").is_none());
}

#[test]
fn gamma_sets_drift_without_naming_constant_drift() {
    let mut a: Borrowed = History::builder().gamma(0.5).build();
    let mut b: Borrowed = History::builder().drift(ConstantDrift::new(0.5)).build();

    for h in [&mut a, &mut b] {
        h.record_winner(&"x", &"y", 1).unwrap();
        h.record_winner(&"y", &"x", 100).unwrap();
        h.converge().unwrap();
    }

    let (ga, gb) = (a.current_skill("x").unwrap(), b.current_skill("x").unwrap());
    assert_eq!((ga.mu(), ga.sigma()), (gb.mu(), gb.sigma()));

    // Control: the shorthand is not a no-op — a different gamma differs.
    let mut c: Borrowed = History::builder().gamma(0.0).build();
    c.record_winner(&"x", &"y", 1).unwrap();
    c.record_winner(&"y", &"x", 100).unwrap();
    c.converge().unwrap();
    assert_ne!(c.current_skill("x").unwrap().sigma(), ga.sigma());
}

#[test]
#[should_panic(expected = "gamma must be finite and non-negative")]
fn a_negative_gamma_is_rejected_rather_than_squared_away() {
    let _: Borrowed = History::builder().gamma(-0.5).build();
}