use db fixture

tests/integration/conftest.py

@@ -380,6 +380,13 @@ async def integration_session(
         yield session
 
 
+@pytest_asyncio.fixture
+async def patched_db_engine(integration_engine: Any) -> AsyncGenerator[None, None]:
+    """Patch the global db engine so create_session() uses the test engine."""
+    with patch("routstr.core.db.engine", integration_engine):
+        yield
+
+
 class DatabaseSnapshot:
     """Utility to capture and compare database states"""
 

tests/integration/test_balance_negative_on_cost_overrun.py

@@ -179,6 +179,7 @@ async def test_full_cost_charged_when_balance_sufficient_for_overrun(
 @pytest.mark.asyncio
 async def test_concurrent_cost_overruns_never_negative(
     integration_session: AsyncSession,
+    patched_db_engine: None,
 ) -> None:
     """Concurrent finalization with cost overruns must never produce negative balance."""
     import asyncio
@@ -302,6 +303,7 @@ async def test_zero_free_balance_overrun_is_safe(
 @pytest.mark.asyncio
 async def test_parallel_requests_no_free_inference(
     integration_session: AsyncSession,
+    patched_db_engine: None,
 ) -> None:
     """Second parallel finalization must be charged even when first depleted free balance."""
     import asyncio

tests/integration/test_reservation_lifecycle.py

@@ -134,7 +134,9 @@ async def test_finalise_releases_reservation_and_charges_balance(
 # ---------------------------------------------------------------------------
 
 @pytest.mark.asyncio
-async def test_concurrent_second_reserve_blocked_when_balance_exhausted() -> None:
+async def test_concurrent_second_reserve_blocked_when_balance_exhausted(
+    patched_db_engine: None,
+) -> None:
     """When two requests race for the same balance, only one succeeds; the other gets 402."""
     cost = 300
     key_hash = f"test_concurrent_{uuid.uuid4().hex}"
@@ -185,7 +187,9 @@ async def test_concurrent_second_reserve_blocked_when_balance_exhausted() -> Non
 # ---------------------------------------------------------------------------
 
 @pytest.mark.asyncio
-async def test_three_parallel_reserves_third_blocked() -> None:
+async def test_three_parallel_reserves_third_blocked(
+    patched_db_engine: None,
+) -> None:
     """Balance covers two reservations exactly; the third concurrent request must be blocked."""
     cost = 100
     key_hash = f"test_three_parallel_{uuid.uuid4().hex}"