tests: dispose engines in app fixture cleanup

tests/conftest.py

@@ -15,11 +15,21 @@
 
 
 @pytest.fixture
-def app(request: pytest.FixtureRequest, tmp_path: Path) -> Flask:
+def app(request: pytest.FixtureRequest, tmp_path: Path) -> t.Generator[Flask]:
     app = Flask(request.module.__name__, instance_path=str(tmp_path / "instance"))
     app.config["SQLALCHEMY_DATABASE_URI"] = "sqlite://"
     app.config["SQLALCHEMY_RECORD_QUERIES"] = False
-    return app
+    yield app
+
+    if app.extensions:
+        db = app.extensions["sqlalchemy"]
+        # Duplicate SQLAlchemy.engines logic to avoid errors when the app
+        # is not initialized properly.
+        if app in db._app_engines:
+            engines = db._app_engines[app]
+            if engines:
+                for engine in engines.values():
+                    engine.dispose()
 
 
 @pytest.fixture

tests/test_metadata.py

@@ -156,6 +156,10 @@ def test_reflect(app: Flask) -> None:
     db.Table("post", sa.Column("id", sa.Integer, primary_key=True), bind_key="post")
     db.create_all()
 
+    # Dispose engines to close connections and avoid warning
+    for engine in db.engines.values():
+        engine.dispose()
+
     del app.extensions["sqlalchemy"]
     db = SQLAlchemy(app)
     assert not db.metadata.tables