Replace fixed sleep delays with active polling in prometheus service test

monitoring/prometheus/service_test.go

@@ -26,8 +26,21 @@ func TestLifecycle(t *testing.T) {
 	port := 1000 + rand.Intn(1000)
 	prometheusService := NewService(t.Context(), fmt.Sprintf(":%d", port), nil)
 	prometheusService.Start()
-	// Give service time to start.
-	time.Sleep(time.Second)
+    // Actively wait until the service responds on /metrics (faster and less flaky than a fixed sleep)
+    deadline := time.Now().Add(3 * time.Second)
+    for {
+        if time.Now().After(deadline) {
+            t.Fatalf("metrics endpoint not ready within timeout")
+        }
+        resp, err := http.Get(fmt.Sprintf("http://localhost:%d/metrics", port))
+        if err == nil {
+            _ = resp.Body.Close()
+            if resp.StatusCode == http.StatusOK {
+                break
+            }
+        }
+        time.Sleep(50 * time.Millisecond)
+    }
 
 	// Query the service to ensure it really started.
 	resp, err := http.Get(fmt.Sprintf("http://localhost:%d/metrics", port))
@@ -36,8 +49,18 @@ func TestLifecycle(t *testing.T) {
 
 	err = prometheusService.Stop()
 	require.NoError(t, err)
-	// Give service time to stop.
-	time.Sleep(time.Second)
+    // Actively wait until the service stops responding on /metrics
+    deadline = time.Now().Add(3 * time.Second)
+    for {
+        if time.Now().After(deadline) {
+            t.Fatalf("metrics endpoint still reachable after timeout")
+        }
+        _, err = http.Get(fmt.Sprintf("http://localhost:%d/metrics", port))
+        if err != nil {
+            break
+        }
+        time.Sleep(50 * time.Millisecond)
+    }
 
 	// Query the service to ensure it really stopped.
 	_, err = http.Get(fmt.Sprintf("http://localhost:%d/metrics", port))