feat: rapidfuzz-based ingredient<->grocery matcher with manual-pin preservation

backend/tests/test_matcher.py

@@ -0,0 +1,44 @@
+import pytest
+
+from app.services.matcher import build_match_pool, rank_candidates
+
+
+def test_build_match_pool_includes_aliases() -> None:
+    ingredients = [
+        {"id": "i1", "name": "Chicken Thighs", "aliases": ["chicken thigh"]},
+        {"id": "i2", "name": "Chicken Breast", "aliases": []},
+    ]
+    pool = build_match_pool(ingredients)
+    # 1 name + 1 alias for i1, 1 name for i2 = 3 entries
+    assert len(pool) == 3
+    assert ("Chicken Thighs", "i1") in pool
+    assert ("chicken thigh", "i1") in pool
+
+
+def test_rank_candidates_top_n_with_threshold() -> None:
+    pool = [
+        ("Chicken Thighs", "i1"),
+        ("chicken thigh", "i1"),
+        ("Chicken Breast", "i2"),
+        ("Pork Chops", "i3"),
+    ]
+    ranked = rank_candidates(
+        target="Foster Farms Chicken Thighs Family Pack",
+        pool=pool,
+        top_n=3,
+        threshold=0.75,
+    )
+    ids = [item["ingredient_id"] for item in ranked]
+    assert ids[0] == "i1"
+    assert all(item["confidence"] >= 0.75 for item in ranked)
+
+
+def test_rank_candidates_drops_below_threshold() -> None:
+    pool = [("Pork Chops", "i3")]
+    ranked = rank_candidates(
+        target="Frosted Flakes Cereal 18oz",
+        pool=pool,
+        top_n=3,
+        threshold=0.75,
+    )
+    assert ranked == []