feat: add DecisionRepository with unit tests

Repository provides upsert, get, delete, and disliked-ID-set queries
for listing decisions. All 6 unit tests pass.

tests/unit/test_decision_repository.py

@@ -0,0 +1,88 @@
+"""Unit tests for DecisionRepository."""
+import pytest
+from sqlalchemy import Engine
+from sqlmodel import SQLModel, Session, create_engine
+
+from models.decision import ListingDecision
+from models.user import User
+from repositories.decision_repository import DecisionRepository
+
+
+@pytest.fixture
+def decision_engine() -> Engine:
+    engine = create_engine(
+        "sqlite:///:memory:",
+        echo=False,
+        connect_args={"check_same_thread": False},
+    )
+    SQLModel.metadata.create_all(engine)
+    with Session(engine) as session:
+        session.add(User(id=1, email="test@example.com"))
+        session.commit()
+    yield engine  # type: ignore[misc]
+    SQLModel.metadata.drop_all(engine)
+
+
+@pytest.fixture
+def repo(decision_engine: Engine) -> DecisionRepository:
+    return DecisionRepository(decision_engine)
+
+
+class TestDecisionRepository:
+    def test_upsert_creates_new_decision(self, repo: DecisionRepository) -> None:
+        result = repo.upsert_decision(
+            user_id=1, listing_id=100, listing_type="RENT", decision="liked"
+        )
+        assert result.decision == "liked"
+        assert result.listing_id == 100
+
+    def test_upsert_updates_existing_decision(self, repo: DecisionRepository) -> None:
+        repo.upsert_decision(
+            user_id=1, listing_id=100, listing_type="RENT", decision="liked"
+        )
+        result = repo.upsert_decision(
+            user_id=1, listing_id=100, listing_type="RENT", decision="disliked"
+        )
+        assert result.decision == "disliked"
+        # Should still be one record
+        all_decisions = repo.get_decisions_for_user(1)
+        assert len(all_decisions) == 1
+
+    def test_get_decisions_for_user(self, repo: DecisionRepository) -> None:
+        repo.upsert_decision(
+            user_id=1, listing_id=100, listing_type="RENT", decision="liked"
+        )
+        repo.upsert_decision(
+            user_id=1, listing_id=200, listing_type="RENT", decision="disliked"
+        )
+        decisions = repo.get_decisions_for_user(1)
+        assert len(decisions) == 2
+
+    def test_delete_decision(self, repo: DecisionRepository) -> None:
+        repo.upsert_decision(
+            user_id=1, listing_id=100, listing_type="RENT", decision="liked"
+        )
+        deleted = repo.delete_decision(
+            user_id=1, listing_id=100, listing_type="RENT"
+        )
+        assert deleted is True
+        assert len(repo.get_decisions_for_user(1)) == 0
+
+    def test_delete_nonexistent_decision(self, repo: DecisionRepository) -> None:
+        deleted = repo.delete_decision(
+            user_id=1, listing_id=999, listing_type="RENT"
+        )
+        assert deleted is False
+
+    def test_get_disliked_listing_ids(self, repo: DecisionRepository) -> None:
+        repo.upsert_decision(
+            user_id=1, listing_id=100, listing_type="RENT", decision="liked"
+        )
+        repo.upsert_decision(
+            user_id=1, listing_id=200, listing_type="RENT", decision="disliked"
+        )
+        repo.upsert_decision(
+            user_id=1, listing_id=300, listing_type="RENT", decision="disliked"
+        )
+        disliked = repo.get_disliked_listing_ids(user_id=1, listing_type="RENT")
+        assert disliked == {200, 300}