Enhance test coverage in test_app.py and test_indexer.py by refining mocking strategies and improving error handling. Update session and file reading mocks for better accuracy, and ensure health check tests correctly assess Meilisearch availability. Streamline argument passing for consistency across tests.

.vscode/settings.json

@@ -0,0 +1,5 @@
+{
+    "python.testing.pytestArgs": [
+        "backend/tests"
+    ]
+}