test(cat): require Rust-owned item information and next-item selection

tests/test_cat_selection_rust_ownership.py

@@ -0,0 +1,68 @@
+"""Fail-first ownership contracts for CAT item information and selection."""
+
+from __future__ import annotations
+
+import numpy as np
+
+import fast_mlsirm._core as core
+from fast_mlsirm.test_design import item_information, select_cat_item
+from fast_mlsirm.types import MLSIRMParams
+
+
+def _bank() -> tuple[MLSIRMParams, np.ndarray]:
+    """Return a small one-dimensional bank for CAT ownership tests."""
+    discrimination = np.array([0.8, 1.1, 1.4, 1.7], dtype=np.float64)
+    bank = MLSIRMParams(
+        theta=np.array([[0.0]], dtype=np.float64),
+        alpha=np.log(discrimination),
+        b=np.array([-1.0, -0.2, 0.4, 1.2], dtype=np.float64),
+        xi=np.zeros((1, 1), dtype=np.float64),
+        zeta=np.zeros((4, 1), dtype=np.float64),
+        tau=-30.0,
+    )
+    return bank, np.zeros(4, dtype=np.int64)
+
+
+def test_public_item_information_uses_rust_numerical_result(monkeypatch) -> None:
+    """Public item information must delegate its numerical result to Rust."""
+    bank, factor_id = _bank()
+    calls: list[tuple[tuple[object, ...], dict[str, object]]] = []
+
+    def fake_information(*args, **kwargs):
+        calls.append((args, kwargs))
+        return [0.125, 0.25, 0.5, 0.75]
+
+    monkeypatch.setattr(core, "cat_item_information", fake_information, raising=False)
+
+    result = item_information(
+        bank,
+        factor_id,
+        theta=np.array([0.25], dtype=np.float64),
+        model="MIRT",
+    )
+
+    assert len(calls) == 1
+    assert np.array_equal(result, np.array([0.125, 0.25, 0.5, 0.75]))
+
+
+def test_public_cat_selection_uses_rust_ranking_result(monkeypatch) -> None:
+    """Next-item argmax/exclusion policy that determines the result must be Rust-owned."""
+    bank, factor_id = _bank()
+    calls: list[tuple[tuple[object, ...], dict[str, object]]] = []
+
+    def fake_selection(*args, **kwargs):
+        calls.append((args, kwargs))
+        return 2
+
+    monkeypatch.setattr(core, "cat_select_item", fake_selection, raising=False)
+
+    selected = select_cat_item(
+        bank,
+        factor_id,
+        theta=np.array([-0.5], dtype=np.float64),
+        administered=np.array([0, 1], dtype=np.int64),
+        model="MIRT",
+    )
+
+    assert len(calls) == 1
+    assert selected == 2