tests: function-scoped engine + frisk session per request

Hver test får sin egen engine (function-scoped) med friske
tabeller (drop_all + create_all). Appen får sin egen session
per request via dependency override — ingen deling af sessions.

admin_user/normal_user opretter data via egen session og
lukker den. client bruger async_sessionmaker i override_get_db.

Ingen _clean_db fixture, ingen outer transaction, ingen
SAVEPOINT — hver test starter blankt og engine.dispose()
rydder op.

backend/tests/conftest.py

@@ -1,4 +1,9 @@
-"""Test fixtures — async database and HTTP client."""
+"""Test fixtures — async database and HTTP client.
+
+Hver test får sin egen engine (function-scoped) med friske tabeller.
+Appen får sin egen session per request via dependency override.
+Ingen delte sessions — ingen "another operation is in progress".
+"""
 
 import pytest
 import pytest_asyncio
@@ -21,71 +26,60 @@ DATABASE_URL = os.getenv(
 )
 
 
-@pytest_asyncio.fixture(scope="session")
+@pytest_asyncio.fixture(autouse=True)
 async def engine():
-    """Create a fresh database for testing."""
+    """Frisk engine per test — skaber tabeller, smider væk bagefter."""
     e = create_async_engine(DATABASE_URL, echo=False)
     async with e.begin() as conn:
         await conn.run_sync(Base.metadata.drop_all)
         await conn.run_sync(Base.metadata.create_all)
     yield e
-    async with e.begin() as conn:
-        await conn.run_sync(Base.metadata.drop_all)
     await e.dispose()
 
 
 @pytest_asyncio.fixture
-async def session(engine):
-    """Per-test database session.
-
-    Data commited her er synlig for appens egen session via HTTP client.
-    Renses automatisk af _clean_db efter hver test.
-    """
+async def client(engine):
+    """HTTP client — appen får en frisk session på testens engine per request."""
     maker = async_sessionmaker(bind=engine, expire_on_commit=False)
+
+    async def override_get_db():
         async with maker() as s:
             yield s
 
-
-@pytest_asyncio.fixture(autouse=True)
-async def _clean_db(engine):
-    """Slet alt data fra alle tabeller efter hver test."""
-    yield
-    async with engine.begin() as conn:
-        for table in reversed(Base.metadata.sorted_tables):
-            await conn.execute(table.delete())
-
-
-@pytest_asyncio.fixture
-async def client():
-    """HTTP client — appen bruger sin egen DB session via get_db()."""
+    app.dependency_overrides[get_db] = override_get_db
     transport = ASGITransport(app=app)
     async with AsyncClient(transport=transport, base_url="http://test") as ac:
         yield ac
+    app.dependency_overrides.clear()
 
 
 @pytest_asyncio.fixture
-async def admin_user(session):
-    """Insert admin user into test DB (ryddes af _clean_db)."""
+async def admin_user(engine):
+    """Insert admin user — frisk session, committer, lukker."""
+    maker = async_sessionmaker(bind=engine, expire_on_commit=False)
+    async with maker() as s:
         u = User(
             username="admin",
             password_hash=hash_password("admin123"),
             role="admin",
         )
-    session.add(u)
-    await session.commit()
+        s.add(u)
+        await s.commit()
         return u
 
 
 @pytest_asyncio.fixture
-async def normal_user(session):
-    """Insert normal user into test DB (ryddes af _clean_db)."""
+async def normal_user(engine):
+    """Insert normal user — frisk session, committer, lukker."""
+    maker = async_sessionmaker(bind=engine, expire_on_commit=False)
+    async with maker() as s:
         u = User(
             username="testuser",
             password_hash=hash_password("test123"),
             role="user",
         )
-    session.add(u)
-    await session.commit()
+        s.add(u)
+        await s.commit()
         return u