tests: add test_calibration.py for apply_affine, save/load round-trip, missing/invalid

Author: Henry Wallace

tests/test_calibration.py

@@ -0,0 +1,50 @@
+"""Tests for affine calibration: apply_affine, load_calibration, save_calibration."""
+
+import json
+from pathlib import Path
+
+import pytest
+
+from tiny_icf.calibration import apply_affine, load_calibration, save_calibration
+
+
+def test_apply_affine_formula():
+    """apply_affine(pred, a, b) == clip(a + b * pred, 0, 1)."""
+    a, b = 0.1, 0.9
+    assert apply_affine(0.0, a, b) == pytest.approx(0.1)
+    assert apply_affine(1.0, a, b) == pytest.approx(1.0)
+    assert apply_affine(0.5, a, b) == pytest.approx(0.1 + 0.9 * 0.5)
+
+
+def test_apply_affine_clipping():
+    """Output is clipped to [0, 1]."""
+    assert apply_affine(2.0, 0.0, 1.0) == 1.0
+    assert apply_affine(-1.0, 0.0, 1.0) == 0.0
+    assert apply_affine(0.5, 1.0, 1.0) == 1.0
+    assert apply_affine(0.5, -0.5, 0.5) == 0.0
+
+
+def test_save_load_roundtrip(tmp_path: Path):
+    """save_calibration then load_calibration returns same (a, b)."""
+    cal_path = tmp_path / "model.pt.cal.json"
+    save_calibration(cal_path, 0.05, 0.95)
+    loaded = load_calibration(cal_path)
+    assert loaded is not None
+    assert loaded == (0.05, 0.95)
+    data = json.loads(cal_path.read_text())
+    assert data["a"] == 0.05 and data["b"] == 0.95
+
+
+def test_load_calibration_missing_returns_none(tmp_path: Path):
+    """load_calibration on missing file returns None."""
+    assert load_calibration(tmp_path / "nonexistent.cal.json") is None
+
+
+def test_load_calibration_invalid_returns_none(tmp_path: Path):
+    """load_calibration on invalid JSON returns None."""
+    bad = tmp_path / "bad.cal.json"
+    bad.write_text("not json")
+    assert load_calibration(bad) is None
+    bad.write_text("{}")
+    # empty dict: get("a", 0.0), get("b", 1.0) so (0.0, 1.0) is valid
+    assert load_calibration(bad) == (0.0, 1.0)