From dd0a792438bb6ef88863e404b3391ab890590636 Mon Sep 17 00:00:00 2001
From: Simon Pasquier <spasquie@redhat.com>
Date: Fri, 30 Jan 2026 16:06:25 +0100
Subject: [PATCH] Add end-to-end tests for Alertmanager and ThanosRuler

Signed-off-by: Simon Pasquier <spasquie@redhat.com>
---
 test/e2e/alertmanager_test.go | 31 +++++++++++++++++++++++++++++++
 test/e2e/main_test.go         |  2 ++
 test/e2e/thanosruler_test.go  | 30 ++++++++++++++++++++++++++++++
 test/framework/thanosruler.go | 11 +++++++++++
 4 files changed, 74 insertions(+)

diff --git a/test/e2e/alertmanager_test.go b/test/e2e/alertmanager_test.go
index 476e72227..983b1691c 100644
--- a/test/e2e/alertmanager_test.go
+++ b/test/e2e/alertmanager_test.go
@@ -2729,3 +2729,34 @@ func testAlertManagerServiceName(t *testing.T) {
 	require.Len(t, svcList.Items, 1)
 	require.Equal(t, svcList.Items[0].Name, svc.Name)
 }
+
+func testAMScaleUpWithoutLabels(t *testing.T) {
+	// Don't run Alertmanager tests in parallel. See
+	// https://github.com/prometheus/alertmanager/issues/1835 for details.
+	ctx := context.Background()
+	testCtx := framework.NewTestCtx(t)
+	defer testCtx.Cleanup(t)
+	ns := framework.CreateNamespace(ctx, t, testCtx)
+	framework.SetupPrometheusRBAC(ctx, t, testCtx, ns)
+
+	name := "test"
+
+	// Create an Alertmanager resource with 1 replica
+	am, err := framework.CreateAlertmanagerAndWaitUntilReady(ctx, framework.MakeBasicAlertmanager(ns, name, 1))
+	require.NoError(t, err)
+
+	// Remove all labels on the StatefulSet using Patch
+	stsName := fmt.Sprintf("alertmanager-%s", name)
+	err = framework.RemoveAllLabelsFromStatefulSet(ctx, stsName, ns)
+	require.NoError(t, err)
+
+	// Scale up the Alertmanager resource to 2 replicas
+	_, err = framework.UpdateAlertmanagerReplicasAndWaitUntilReady(ctx, am.Name, ns, 2)
+	require.NoError(t, err)
+
+	// Verify the StatefulSet now has labels again (restored by the operator)
+	stsClient := framework.KubeClient.AppsV1().StatefulSets(ns)
+	sts, err := stsClient.Get(ctx, stsName, metav1.GetOptions{})
+	require.NoError(t, err)
+	require.NotEmpty(t, sts.GetLabels(), "expected labels to be restored on the StatefulSet by the operator")
+}
diff --git a/test/e2e/main_test.go b/test/e2e/main_test.go
index 9fb5f6ebd..899425963 100644
--- a/test/e2e/main_test.go
+++ b/test/e2e/main_test.go
@@ -251,6 +251,7 @@ func testAllNSAlertmanager(t *testing.T) {
 		"AMTemplateReloadConfig":                  testAMTmplateReloadConfig,
 		"AMStatusScale":                           testAlertmanagerStatusScale,
 		"AMServiceName":                           testAlertManagerServiceName,
+		"AMScaleUpWithoutLabels":                  testAMScaleUpWithoutLabels,
 	}
 
 	for name, f := range testFuncs {
@@ -342,6 +343,7 @@ func testAllNSThanosRuler(t *testing.T) {
 		"ThanosRulerCheckStorageClass":                  testTRCheckStorageClass,
 		"ThanosRulerServiceName":                        testThanosRulerServiceName,
 		"ThanosRulerStateless":                          testThanosRulerStateless,
+		"ThanosRulerScaleUpWithoutLabels":               testThanosRulerScaleUpWithoutLabels,
 	}
 	for name, f := range testFuncs {
 		t.Run(name, f)
diff --git a/test/e2e/thanosruler_test.go b/test/e2e/thanosruler_test.go
index 8538f5586..1d4fa10d0 100644
--- a/test/e2e/thanosruler_test.go
+++ b/test/e2e/thanosruler_test.go
@@ -636,3 +636,33 @@ func testThanosRulerStateless(t *testing.T) {
 	err = framework.WaitForPrometheusFiringAlert(context.Background(), ns, promSVC.Name, testAlert)
 	require.NoError(t, err)
 }
+
+func testThanosRulerScaleUpWithoutLabels(t *testing.T) {
+	t.Parallel()
+	ctx := context.Background()
+	testCtx := framework.NewTestCtx(t)
+	defer testCtx.Cleanup(t)
+	ns := framework.CreateNamespace(ctx, t, testCtx)
+	framework.SetupPrometheusRBAC(ctx, t, testCtx, ns)
+
+	name := "test"
+
+	// Create a ThanosRuler resource with 1 replica
+	tr, err := framework.CreateThanosRulerAndWaitUntilReady(ctx, ns, framework.MakeBasicThanosRuler(name, 1, "http://test.example.com"))
+	require.NoError(t, err)
+
+	// Remove all labels on the StatefulSet using Patch
+	stsName := fmt.Sprintf("thanos-ruler-%s", name)
+	err = framework.RemoveAllLabelsFromStatefulSet(ctx, stsName, ns)
+	require.NoError(t, err)
+
+	// Scale up the ThanosRuler resource to 2 replicas
+	_, err = framework.UpdateThanosRulerReplicasAndWaitUntilReady(ctx, tr.Name, ns, 2)
+	require.NoError(t, err)
+
+	// Verify the StatefulSet now has labels again (restored by the operator)
+	stsClient := framework.KubeClient.AppsV1().StatefulSets(ns)
+	sts, err := stsClient.Get(ctx, stsName, metav1.GetOptions{})
+	require.NoError(t, err)
+	require.NotEmpty(t, sts.GetLabels(), "expected labels to be restored on the StatefulSet by the operator")
+}
diff --git a/test/framework/thanosruler.go b/test/framework/thanosruler.go
index a1ddb9081..91d27f073 100644
--- a/test/framework/thanosruler.go
+++ b/test/framework/thanosruler.go
@@ -108,6 +108,17 @@ func (f *Framework) PatchThanosRuler(ctx context.Context, name, ns string, spec
 	return tr, nil
 }
 
+func (f *Framework) UpdateThanosRulerReplicasAndWaitUntilReady(ctx context.Context, name, ns string, replicas int32) (*monitoringv1.ThanosRuler, error) {
+	return f.PatchThanosRulerAndWaitUntilReady(
+		ctx,
+		name,
+		ns,
+		monitoringv1.ThanosRulerSpec{
+			Replicas: ptr.To(replicas),
+		},
+	)
+}
+
 func (f *Framework) WaitForThanosRulerReady(ctx context.Context, ns string, tr *monitoringv1.ThanosRuler, timeout time.Duration) error {
 	expected := *tr.Spec.Replicas