add test for fastapi prometheus middleware

Author: bisgaard-itis

packages/service-library/tests/fastapi/test_prometheus_middleware.py

@@ -0,0 +1,27 @@
+from collections.abc import AsyncIterable
+
+import pytest
+from asgi_lifespan import LifespanManager
+from fastapi import FastAPI
+from httpx import AsyncClient
+from servicelib.fastapi.monitoring import setup_prometheus_instrumentation
+
+
+@pytest.fixture
+async def app(app: FastAPI) -> AsyncIterable[FastAPI]:
+    """
+    Fixture that sets up the Prometheus middleware in the FastAPI app.
+    """
+    setup_prometheus_instrumentation(app)
+    async with LifespanManager(app):
+        yield app
+
+
+async def test_metrics_endpoint(client: AsyncClient, app: FastAPI):
+    """
+    Test that the /metrics endpoint is available and returns Prometheus metrics.
+    """
+    response = await client.get("/metrics")
+    assert response.status_code == 200
+    assert "# HELP" in response.text
+    assert "# TYPE" in response.text