test: ensure /metrics route for micro-services (refs #4)

Author: pmcfadin

tests/services/test_prometheus_metrics_route.py

@@ -0,0 +1,36 @@
+from importlib import reload
+from types import ModuleType
+
+import pytest
+from fastapi import FastAPI
+from app.utils.observability import Instrumentator  # type: ignore
+
+# List of (module path, attribute name) tuples for each micro-service FastAPI app
+SERVICE_MODULES = [
+    ("app.main_user", "service_app"),
+    ("app.main_comment", "service_app"),
+    ("app.main_video", "service_app"),
+    ("app.main_reco", "service_app"),
+    ("app.main_search", "service_app"),
+    ("app.main_moderation", "service_app"),
+]
+
+
+@pytest.mark.parametrize("module_path, attr", SERVICE_MODULES)
+def test_metrics_route_present_once(module_path: str, attr: str):
+    """Ensure each micro-service exposes exactly one /metrics endpoint."""
+
+    # Reload observability module so that its module-level flags are reset for each service
+    reload(__import__("app.utils.observability", fromlist=["*"]))
+
+    mod: ModuleType = __import__(module_path, fromlist=[attr])
+    app: FastAPI = getattr(mod, attr)
+
+    if Instrumentator is None:  # pragma: no cover
+        pytest.skip("prometheus_fastapi_instrumentator not installed; skipping metrics route test")
+
+    metrics_routes = [r for r in app.routes if getattr(r, "path", None) == "/metrics"]
+
+    assert len(metrics_routes) == 1, (
+        f"Expected exactly one /metrics route in {module_path}, found {len(metrics_routes)}"
+    )