fix: Update HTTP status code for unprocessable entity and improve test database setup

tests/unit/conftest.py

@@ -68,10 +68,13 @@ def setup_database() -> Generator[None, None, None]:
 
 @pytest.fixture()
 def db_session() -> Generator[Session, None, None]:
+    Base.metadata.drop_all(bind=engine)
+    Base.metadata.create_all(bind=engine)
     session = TestingSessionLocal()
     try:
         yield session
     finally:
+        session.rollback()
         session.close()