Merge branch 'test/close-coverage-gaps'

Cover non-finite results and color-group disjointness, closing the two
test gaps #26 named.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_011hcFjNDmHXZF8URGLku5zZ

src/color_group.rs

@@ -191,3 +191,121 @@ mod tests {
         assert_eq!(cg.total_events(), 4);
     }
 }
+
+#[cfg(test)]
+mod properties {
+    use std::collections::HashSet;
+
+    use proptest::prelude::*;
+
+    use super::*;
+
+    /// The property the whole parallel sweep rests on: two events sharing a
+    /// competitor must never land in the same color, because a color group is
+    /// run concurrently and two events touching one competitor would race.
+    ///
+    /// Hand-written cases cover the shapes someone thought of. This covers the
+    /// ones nobody did — the correctness of `sweep_color_groups` depends on it
+    /// holding for every input, not for five.
+    fn check(events: &[Vec<usize>]) {
+        let groups = color_greedy(events.len(), |ev| {
+            events[ev]
+                .iter()
+                .copied()
+                .map(Index::from)
+                .collect::<Vec<_>>()
+        });
+
+        // Disjointness *between events* within a color. Deduplicated per
+        // event, because one event legitimately naming a competitor twice is
+        // not a collision — `color_greedy` collects each event's members into
+        // a set for exactly that reason.
+        for color in 0..groups.n_colors() {
+            let mut seen: HashSet<usize> = HashSet::new();
+            for &ev in &groups.groups[color] {
+                let members: HashSet<usize> = events[ev].iter().copied().collect();
+                for competitor in members {
+                    assert!(
+                        seen.insert(competitor),
+                        "competitor {competitor} shared by two events in color {color}"
+                    );
+                }
+            }
+        }
+
+        // Every event is assigned exactly once. Without this, a partition that
+        // dropped events would satisfy disjointness trivially.
+        let mut assigned: Vec<usize> = groups.groups.iter().flatten().copied().collect();
+        assigned.sort_unstable();
+        assert_eq!(assigned, (0..events.len()).collect::<Vec<_>>());
+        assert_eq!(groups.total_events(), events.len());
+
+        // No empty colors: one would waste a sweep and make `n_colors`
+        // misleading.
+        for (color, group) in groups.groups.iter().enumerate() {
+            assert!(!group.is_empty(), "color {color} is empty");
+        }
+
+        // Contiguity is not a property of `color_greedy` — it holds only after
+        // `recompute_color_groups` reorders the events so each color occupies
+        // one range. What must always hold is that the reorder is *possible*:
+        // relabelling events in group order yields contiguous groups. The
+        // parallel sweep slices `&mut` sub-ranges from those, so if this ever
+        // failed the reorder would produce overlapping ranges.
+        let mut next = 0usize;
+        let relabelled: Vec<Vec<usize>> = groups
+            .groups
+            .iter()
+            .map(|group| {
+                group
+                    .iter()
+                    .map(|_| {
+                        let i = next;
+                        next += 1;
+                        i
+                    })
+                    .collect()
+            })
+            .collect();
+        assert!(ColorGroups { groups: relabelled }.groups_are_contiguous());
+    }
+
+    proptest! {
+        #![proptest_config(ProptestConfig::with_cases(512))]
+
+        /// Small competitor pool, so collisions are common and colors are
+        /// forced to multiply.
+        #[test]
+        fn colors_are_disjoint_on_a_dense_pool(
+            events in prop::collection::vec(
+                prop::collection::vec(0usize..6, 1..4),
+                0..20,
+            )
+        ) {
+            check(&events);
+        }
+
+        /// Wide pool, so most events are independent and land in one color.
+        #[test]
+        fn colors_are_disjoint_on_a_sparse_pool(
+            events in prop::collection::vec(
+                prop::collection::vec(0usize..200, 1..6),
+                0..30,
+            )
+        ) {
+            check(&events);
+        }
+
+        /// Repeated competitors within one event must not confuse the
+        /// member-set bookkeeping.
+        #[test]
+        fn colors_are_disjoint_with_repeated_members(
+            events in prop::collection::vec(
+                prop::collection::vec(0usize..3, 1..8),
+                0..15,
+            )
+        ) {
+            check(&events);
+        }
+    }
+}

tests/non_finite_results.rs

@@ -0,0 +1,117 @@
+//! Inference must report numerical breakdown rather than call it convergence.
+//!
+//! The boundary rejects inputs that are *not numbers*, but finite inputs can
+//! still overflow during inference — `beta.powi(2)` at 1e300 is infinite, and
+//! infinity minus infinity is NaN. `NonFiniteResult` is the guard for that, and
+//! it matters because the alternative is silent: NaN fails every comparison, so
+//! a naive `step < epsilon` check reads a NaN step as *converged*.
+//!
+//! That is why the crate has `step_converged` / `step_is_finite` rather than
+//! `!tuple_gt(..)`. These tests pin the guard from outside.
+
+use smallvec::smallvec;
+use trueskill_tt::{Event, Gaussian, History, InferenceError, Member, Outcome, Team};
+
+fn scored_fit(
+    sigma: f64,
+    beta: f64,
+    score_sigma: f64,
+    scores: [f64; 2],
+) -> Result<bool, InferenceError> {
+    let mut h = History::builder()
+        .mu(0.0)
+        .sigma(sigma)
+        .beta(beta)
+        .score_sigma(score_sigma)
+        .build();
+    h.add_events(vec![Event {
+        time: 1i64,
+        teams: smallvec![
+            Team::with_members([Member::new("a")]),
+            Team::with_members([Member::new("b")]),
+        ],
+        outcome: Outcome::scores(scores),
+    }])?;
+    h.converge().map(|r| r.converged)
+}
+
+/// Every one of these is built from finite, individually legal parameters. The
+/// overflow happens inside inference, which is exactly the case the boundary
+/// checks cannot catch.
+///
+/// Matched rather than merely `is_err()`: an assertion that only checks "some
+/// error" would keep passing if these started failing at the boundary for an
+/// unrelated reason, and would then be testing nothing.
+#[test]
+fn overflow_during_inference_is_reported_not_hidden() {
+    let cases: [(&str, f64, f64, f64, [f64; 2]); 5] = [
+        ("huge sigma", 1e300, 1.0, 1.0, [3.0, 1.0]),
+        ("huge beta", 6.0, 1e300, 1.0, [3.0, 1.0]),
+        ("tiny sigma", 1e-300, 1.0, 1.0, [3.0, 1.0]),
+        ("tiny score_sigma", 6.0, 1.0, 1e-300, [3.0, 1.0]),
+        ("huge scores", 6.0, 1.0, 1.0, [1e308, -1e308]),
+    ];
+
+    for (name, sigma, beta, score_sigma, scores) in cases {
+        match scored_fit(sigma, beta, score_sigma, scores) {
+            Err(InferenceError::NonFiniteResult { context, step }) => {
+                assert_eq!(context, "History::converge", "{name}");
+                assert!(
+                    !step.0.is_finite() || !step.1.is_finite(),
+                    "{name}: reported NonFiniteResult with a finite step {step:?}"
+                );
+            }
+            other => panic!("{name}: expected NonFiniteResult, got {other:?}"),
+        }
+    }
+}
+
+/// The trap the invariant exists for: NaN fails every comparison, so a naive
+/// `step < epsilon` test reads a NaN step as converged. A breakdown must never
+/// come back as a successful fit.
+#[test]
+fn a_broken_fit_is_never_reported_as_converged() {
+    let mut h = History::builder().build();
+    h.add_events(vec![Event {
+        time: 1i64,
+        teams: smallvec![
+            Team::with_members([Member::new("a").with_prior(Gaussian::from_ms(1e300, 1e-300))]),
+            Team::with_members([Member::new("b")]),
+        ],
+        outcome: Outcome::winner(0, 2),
+    }])
+    .unwrap();
+
+    let err = h.converge().unwrap_err();
+    assert!(
+        matches!(err, InferenceError::NonFiniteResult { .. }),
+        "a breakdown must not be reported as convergence: {err:?}"
+    );
+
+    // `converge_partial` must not launder it into an `Ok` either — the
+    // permissive path is permissive about *stopping short*, not about NaN.
+    let mut h2 = History::builder().build();
+    h2.add_events(vec![Event {
+        time: 1i64,
+        teams: smallvec![
+            Team::with_members([Member::new("a").with_prior(Gaussian::from_ms(1e300, 1e-300))]),
+            Team::with_members([Member::new("b")]),
+        ],
+        outcome: Outcome::winner(0, 2),
+    }])
+    .unwrap();
+    assert!(matches!(
+        h2.converge_partial().unwrap_err(),
+        InferenceError::NonFiniteResult { .. }
+    ));
+}
+
+/// The neighbouring case, so the tests above cannot pass by the fit simply
+/// always failing: ordinary extreme-but-workable parameters still converge.
+#[test]
+fn merely_extreme_parameters_still_converge() {
+    assert!(scored_fit(1e6, 1.0, 1.0, [3.0, 1.0]).unwrap());
+    assert!(scored_fit(1e-6, 1.0, 1.0, [3.0, 1.0]).unwrap());
+    assert!(scored_fit(6.0, 1.0, 1e6, [3.0, 1.0]).unwrap());
+    assert!(scored_fit(6.0, 1.0, 1.0, [1e150, -1e150]).unwrap());
+}