Add trafficdist package for handling reconciliation of new field

staging/src/k8s.io/endpointslice/trafficdist/trafficdist.go

@@ -0,0 +1,143 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+// trafficdist handles reconciliation of hints for trafficDistribution field.
+package trafficdist
+
+import (
+	corev1 "k8s.io/api/core/v1"
+	discoveryv1 "k8s.io/api/discovery/v1"
+)
+
+// ReconcileHints will reconcile hints for the given EndpointSlices.
+//
+// EndpointSlice resources within slicesUnchanged will not be modified.
+func ReconcileHints(trafficDistribution *string, slicesToCreate, slicesToUpdate, slicesUnchanged []*discoveryv1.EndpointSlice) ([]*discoveryv1.EndpointSlice, []*discoveryv1.EndpointSlice, []*discoveryv1.EndpointSlice) {
+	var h heuristic = &defaultHeuristic{}
+
+	if trafficDistribution != nil && *trafficDistribution == corev1.ServiceTrafficDistributionPreferClose {
+		h = &preferCloseHeuristic{}
+	}
+
+	// Identify the Unchanged slices that need an update because of missing or
+	// incorrect zone hint.
+	//
+	// Uses filtering in place to remove any endpoints that are no longer
+	// unchanged and need to be moved to slicesToUpdate
+	// (https://github.com/golang/go/wiki/SliceTricks#filter-in-place)
+	j := 0
+	for _, slice := range slicesUnchanged {
+		if h.needsUpdate(slice) {
+			// Unchanged slices are direct copies from informer cache. We need to deep
+			// copy an unchanged slice before making any modifications to it so that we do
+			// not modify the slice within the informer cache.
+			slicesToUpdate = append(slicesToUpdate, slice.DeepCopy())
+		} else {
+			slicesUnchanged[j] = slice
+			j++
+		}
+	}
+	// Truncate slicesUnchanged so it only includes slices that are still
+	// unchanged.
+	slicesUnchanged = slicesUnchanged[:j]
+
+	// Add zone hints to all slices that need to be created or updated.
+	for _, slice := range slicesToCreate {
+		h.update(slice)
+	}
+	for _, slice := range slicesToUpdate {
+		h.update(slice)
+	}
+
+	return slicesToCreate, slicesToUpdate, slicesUnchanged
+}
+
+type heuristic interface {
+	needsUpdate(*discoveryv1.EndpointSlice) bool
+	update(*discoveryv1.EndpointSlice)
+}
+
+// endpointReady returns true if an Endpoint has the Ready condition set to
+// true.
+func endpointReady(endpoint discoveryv1.Endpoint) bool {
+	return endpoint.Conditions.Ready != nil && *endpoint.Conditions.Ready
+}
+
+// defaultHeuristic means cluster wide routing, hence it will remove any hints
+// present in the EndpointSlice.
+type defaultHeuristic struct {
+}
+
+// needsUpdate returns true if any endpoint in the slice has a zone hint.
+func (defaultHeuristic) needsUpdate(slice *discoveryv1.EndpointSlice) bool {
+	if slice == nil {
+		return false
+	}
+	for _, endpoint := range slice.Endpoints {
+		if endpoint.Hints != nil {
+			return true
+		}
+	}
+	return false
+}
+
+// update removes zone hints from all endpoints.
+func (defaultHeuristic) update(slice *discoveryv1.EndpointSlice) {
+	for i := range slice.Endpoints {
+		slice.Endpoints[i].Hints = nil
+	}
+}
+
+// preferCloseHeuristic adds
+type preferCloseHeuristic struct {
+}
+
+// needsUpdate returns true if any ready endpoint in the slice has a
+// missing or incorrect hint.
+func (preferCloseHeuristic) needsUpdate(slice *discoveryv1.EndpointSlice) bool {
+	if slice == nil {
+		return false
+	}
+	for _, endpoint := range slice.Endpoints {
+		if !endpointReady(endpoint) {
+			continue
+		}
+		var zone string
+		if endpoint.Zone != nil {
+			zone = *endpoint.Zone
+		}
+
+		if endpoint.Hints == nil || len(endpoint.Hints.ForZones) != 1 || endpoint.Hints.ForZones[0].Name != zone {
+			return true
+		}
+	}
+	return false
+}
+
+// update adds a same zone topology hint for all ready endpoints
+func (preferCloseHeuristic) update(slice *discoveryv1.EndpointSlice) {
+	for i, endpoint := range slice.Endpoints {
+		if !endpointReady(endpoint) {
+			continue
+		}
+
+		var zone string
+		if endpoint.Zone != nil {
+			zone = *endpoint.Zone
+		}
+		slice.Endpoints[i].Hints = &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: zone}}}
+	}
+}

staging/src/k8s.io/endpointslice/trafficdist/trafficdist_test.go

@@ -0,0 +1,470 @@
+/*
+Copyright 2024 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package trafficdist
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"github.com/google/go-cmp/cmp/cmpopts"
+	corev1 "k8s.io/api/core/v1"
+	discoveryv1 "k8s.io/api/discovery/v1"
+	"k8s.io/utils/ptr"
+)
+
+func TestReconcileHints_trafficDistribution_is_PreferClose(t *testing.T) {
+	testCases := []struct {
+		name string
+
+		trafficDistribution *string
+		slicesToCreate      []*discoveryv1.EndpointSlice
+		slicesToUpdate      []*discoveryv1.EndpointSlice
+		slicesUnchanged     []*discoveryv1.EndpointSlice
+
+		wantSlicesToCreate  []*discoveryv1.EndpointSlice
+		wantSlicesToUpdate  []*discoveryv1.EndpointSlice
+		wantSlicesUnchanged []*discoveryv1.EndpointSlice
+	}{
+		{
+			name:                "should set same zone hints",
+			trafficDistribution: ptrTo(corev1.ServiceTrafficDistributionPreferClose),
+			slicesToCreate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.4"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			slicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.6"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.7"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.8"},
+							Zone:       ptr.To("zone-c"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			wantSlicesToCreate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+						{
+							Addresses:  []string{"10.0.0.4"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}},
+						},
+					},
+				},
+			},
+			wantSlicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+						{
+							Addresses:  []string{"10.0.0.6"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.7"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}},
+						},
+						{
+							Addresses:  []string{"10.0.0.8"},
+							Zone:       ptr.To("zone-c"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-c"}}},
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                "incorrect hints should be corrected",
+			trafficDistribution: ptrTo(corev1.ServiceTrafficDistributionPreferClose),
+			slicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}}, // incorrect hint as per new heuristic
+						},
+					},
+				},
+			},
+			slicesUnchanged: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-c"}}},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							Zone:       ptr.To("zone-c"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			wantSlicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							Zone:       ptr.To("zone-c"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-c"}}},
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                "unready endpoints should not trigger updates",
+			trafficDistribution: ptrTo(corev1.ServiceTrafficDistributionPreferClose),
+			slicesUnchanged: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(false)}, // endpoint is not ready
+						},
+					},
+				},
+			},
+			wantSlicesUnchanged: []*discoveryv1.EndpointSlice{ // ... so there should be no updates
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(false)},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			gotSlicesToCreate, gotSlicesToUpdate, gotSlicesUnchanged := ReconcileHints(tc.trafficDistribution, tc.slicesToCreate, tc.slicesToUpdate, tc.slicesUnchanged)
+
+			if diff := cmp.Diff(tc.wantSlicesToCreate, gotSlicesToCreate, cmpopts.EquateEmpty()); diff != "" {
+				t.Errorf("ReconcileHints(...) returned unexpected diff in 'slicesToCreate': (-want, +got)\n%v", diff)
+			}
+			if diff := cmp.Diff(tc.wantSlicesToUpdate, gotSlicesToUpdate, cmpopts.EquateEmpty()); diff != "" {
+				t.Errorf("ReconcileHints(...) returned unexpected diff in 'slicesToUpdate': (-want, +got)\n%v", diff)
+			}
+			if diff := cmp.Diff(tc.wantSlicesUnchanged, gotSlicesUnchanged, cmpopts.EquateEmpty()); diff != "" {
+				t.Errorf("ReconcileHints(...) returned unexpected diff in 'slicesUnchanged': (-want, +got)\n%v", diff)
+			}
+		})
+	}
+}
+
+func TestReconcileHints_trafficDistribution_is_nil_or_empty(t *testing.T) {
+	testCases := []struct {
+		name string
+
+		trafficDistribution *string
+		slicesToCreate      []*discoveryv1.EndpointSlice
+		slicesToUpdate      []*discoveryv1.EndpointSlice
+		slicesUnchanged     []*discoveryv1.EndpointSlice
+
+		wantSlicesToCreate  []*discoveryv1.EndpointSlice
+		wantSlicesToUpdate  []*discoveryv1.EndpointSlice
+		wantSlicesUnchanged []*discoveryv1.EndpointSlice
+	}{
+		{
+			name:                "trafficDistribution='' should remove zone hints",
+			trafficDistribution: ptrTo(""),
+			slicesToCreate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+					},
+				},
+			},
+			slicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+					},
+				},
+			},
+			wantSlicesToCreate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.1"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+						{
+							Addresses:  []string{"10.0.0.2"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.3"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+			wantSlicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+		},
+		{
+			name:                "trafficDistribution=nil should remove zone hints",
+			trafficDistribution: nil,
+			slicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-a"}}},
+						},
+					},
+				},
+			},
+			slicesUnchanged: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.6"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+							Hints:      &discoveryv1.EndpointHints{ForZones: []discoveryv1.ForZone{{Name: "zone-b"}}},
+						},
+					},
+				},
+			},
+			wantSlicesToUpdate: []*discoveryv1.EndpointSlice{
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.5"},
+							Zone:       ptr.To("zone-a"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+				{
+					Endpoints: []discoveryv1.Endpoint{
+						{
+							Addresses:  []string{"10.0.0.6"},
+							Zone:       ptr.To("zone-b"),
+							Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+						},
+					},
+				},
+			},
+		},
+	}
+
+	for _, tc := range testCases {
+		t.Run(tc.name, func(t *testing.T) {
+			gotSlicesToCreate, gotSlicesToUpdate, gotSlicesUnchanged := ReconcileHints(tc.trafficDistribution, tc.slicesToCreate, tc.slicesToUpdate, tc.slicesUnchanged)
+
+			if diff := cmp.Diff(tc.wantSlicesToCreate, gotSlicesToCreate, cmpopts.EquateEmpty()); diff != "" {
+				t.Errorf("ReconcileHints(...) returned unexpected diff in 'slicesToCreate': (-want, +got)\n%v", diff)
+			}
+			if diff := cmp.Diff(tc.wantSlicesToUpdate, gotSlicesToUpdate, cmpopts.EquateEmpty()); diff != "" {
+				t.Errorf("ReconcileHints(...) returned unexpected diff in 'slicesToUpdate': (-want, +got)\n%v", diff)
+			}
+			if diff := cmp.Diff(tc.wantSlicesUnchanged, gotSlicesUnchanged, cmpopts.EquateEmpty()); diff != "" {
+				t.Errorf("ReconcileHints(...) returned unexpected diff in 'slicesUnchanged': (-want, +got)\n%v", diff)
+			}
+		})
+	}
+}
+
+// Ensure that the EndpointSlice objects within `slicesUnchanged` don't get modified.
+func TestReconcileHints_doesNotMutateUnchangedSlices(t *testing.T) {
+	originalEps := &discoveryv1.EndpointSlice{
+		Endpoints: []discoveryv1.Endpoint{
+			{
+				Addresses:  []string{"10.0.0.1"},
+				Zone:       ptr.To("zone-a"),
+				Conditions: discoveryv1.EndpointConditions{Ready: ptr.To(true)},
+			},
+		},
+	}
+	clonedEps := originalEps.DeepCopy()
+
+	// originalEps should not get modified.
+	ReconcileHints(ptrTo(corev1.ServiceTrafficDistributionPreferClose), nil, nil, []*discoveryv1.EndpointSlice{originalEps})
+	if diff := cmp.Diff(clonedEps, originalEps); diff != "" {
+		t.Errorf("ReconcileHints(...) modified objects within slicesUnchanged, want objects within slicesUnchanged to remain unmodified: (-want, +got)\n%v", diff)
+	}
+}
+
+func ptrTo[T any](obj T) *T {
+	return &obj
+}