Add unit tests for pkg/utils/pager

Author: timebertt

pkg/utils/pager/pager.go

@@ -32,8 +32,13 @@ const (
 	defaultPageBufferSize = 10
 )
 
+// lister is the subset of client.Reader that ListPager uses.
+type lister interface {
+	List(ctx context.Context, list client.ObjectList, opts ...client.ListOption) error
+}
+
 // New creates a new pager from the provided reader using the default options.
-func New(reader client.Reader) *ListPager {
+func New(reader lister) *ListPager {
 	return &ListPager{
 		Reader:         reader,
 		PageSize:       defaultPageSize,
@@ -48,7 +53,7 @@ func New(reader client.Reader) *ListPager {
 // Exception: this ListPager also fixes the `specifying resource version is not allowed when using continue` error
 // in EachListItem and EachListItemWithAlloc.
 type ListPager struct {
-	Reader client.Reader
+	Reader lister
 
 	// PageSize is the maximum number of objects to retrieve in individual list calls.
 	// If a client.Limit option is passed, the pager uses the option's value instead.

pkg/utils/pager/pager_suite_test.go

@@ -0,0 +1,29 @@
+/*
+Copyright 2025 Tim Ebert.
+
+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 pager_test
+
+import (
+	"testing"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+)
+
+func TestPager(t *testing.T) {
+	RegisterFailHandler(Fail)
+	RunSpecs(t, "Pager Suite")
+}

pkg/utils/pager/pager_test.go

@@ -0,0 +1,275 @@
+/*
+Copyright 2025 Tim Ebert.
+
+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 pager_test
+
+import (
+	"context"
+	"fmt"
+	"strconv"
+	"time"
+
+	. "github.com/onsi/ginkgo/v2"
+	. "github.com/onsi/gomega"
+	gomegatypes "github.com/onsi/gomega/types"
+	corev1 "k8s.io/api/core/v1"
+	metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
+	"sigs.k8s.io/controller-runtime/pkg/client"
+
+	. "github.com/timebertt/kubernetes-controller-sharding/pkg/utils/pager"
+	. "github.com/timebertt/kubernetes-controller-sharding/pkg/utils/test/matchers"
+)
+
+var _ = Describe("ListPager", func() {
+	const (
+		pageSize    = 2
+		pageCount   = 5
+		objectCount = 9
+	)
+
+	var (
+		ctx context.Context
+
+		allPods []corev1.Pod
+
+		reader *lister
+		pager  *ListPager
+	)
+
+	BeforeEach(func() {
+		ctx = context.Background()
+
+		allPods = podSlice(0, objectCount)
+
+		reader = &lister{allPods: allPods}
+
+		pager = New(reader)
+		pager.PageSize = pageSize
+		pager.PageBufferSize = 2
+	})
+
+	It("should page all objects", func() {
+		var pods []*corev1.Pod
+
+		Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+			pods = append(pods, obj.(*corev1.Pod))
+			return nil
+		})).To(Succeed())
+
+		Expect(pods).To(havePods(1, objectCount))
+
+		Expect(reader.calls).To(Equal(pageCount))
+	})
+
+	It("should page objects with the custom limit", func() {
+		var pods []client.Object
+
+		i := 0
+		Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+			if obj != &allPods[i] {
+				return fmt.Errorf("the pager should reuse the object")
+			}
+			i++
+			pods = append(pods, obj)
+			return nil
+		}, client.Limit(objectCount+1))).To(Succeed())
+
+		Expect(pods).To(havePods(1, objectCount))
+
+		Expect(reader.calls).To(Equal(1))
+	})
+
+	It("should fail due to negative page size", func() {
+		pager.PageSize = -1
+		Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+			return nil
+		})).To(MatchError(ContainSubstring("PageSize must be >= 0")))
+	})
+
+	It("should fail due to negative page buffer size", func() {
+		pager.PageBufferSize = -1
+		Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+			return nil
+		})).To(MatchError(ContainSubstring("PageBufferSize must be >= 0")))
+	})
+
+	It("should return the lister error", func() {
+		Expect(pager.EachListItem(ctx, &corev1.ConfigMapList{}, func(obj client.Object) error {
+			return nil
+		})).To(MatchError("expected *corev1.PodList, got *v1.ConfigMapList"))
+	})
+
+	It("should return the iterator error", func() {
+		Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+			if obj.GetName() == "pod-5" {
+				return fmt.Errorf("foo")
+			}
+			return nil
+		})).To(MatchError("foo"))
+	})
+
+	It("should cancel the operation when the context is canceled", func(specCtx SpecContext) {
+		done := make(chan struct{})
+
+		blockConsumer := make(chan struct{})
+		defer close(blockConsumer)
+
+		ctx, cancel := context.WithCancel(specCtx)
+		go func() {
+			defer GinkgoRecover()
+
+			Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+				<-blockConsumer
+				return nil
+			})).To(MatchError(context.Canceled))
+
+			close(done)
+		}()
+
+		cancel()
+		Eventually(specCtx, done).Should(BeClosed())
+	}, SpecTimeout(time.Second))
+
+	It("should buffer the configured number of pages", func(specCtx SpecContext) {
+		done := make(chan struct{})
+
+		ctx, cancel := context.WithCancel(specCtx)
+		go func() {
+			defer GinkgoRecover()
+
+			Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+				<-ctx.Done()
+				return nil
+			})).To(MatchError(context.Canceled))
+
+			close(done)
+		}()
+
+		Eventually(specCtx, func() int {
+			return reader.calls
+		}).Should(BeEquivalentTo(pager.PageBufferSize + 2)) // consumer takes one chunk out and one chunk is produced but blocked
+
+		cancel()
+		Eventually(specCtx, done).Should(BeClosed())
+	}, SpecTimeout(time.Second))
+
+	It("should correctly handle the resourceVersion fields", func() {
+		Expect(pager.EachListItem(ctx, &corev1.PodList{}, func(obj client.Object) error {
+			return nil
+		}, &client.ListOptions{Raw: &metav1.ListOptions{
+			ResourceVersion:      "0",
+			ResourceVersionMatch: "NotOlderThan",
+		}})).To(Succeed())
+	})
+
+	Describe("#EachListItemWithAlloc", func() {
+		It("should page all objects", func() {
+			var pods []client.Object
+
+			i := 0
+			Expect(pager.EachListItemWithAlloc(ctx, &corev1.PodList{}, func(obj client.Object) error {
+				if obj == &allPods[i] {
+					return fmt.Errorf("the pager should copy the object")
+				}
+				i++
+				pods = append(pods, obj)
+				return nil
+			})).To(Succeed())
+
+			Expect(pods).To(havePods(1, objectCount))
+
+			Expect(reader.calls).To(Equal(pageCount))
+		})
+	})
+})
+
+type lister struct {
+	allPods []corev1.Pod
+	calls   int
+
+	previousList client.ObjectList
+}
+
+func (l *lister) List(_ context.Context, list client.ObjectList, opts ...client.ListOption) error {
+	l.calls++
+
+	if list == l.previousList {
+		return fmt.Errorf("the pager should not reuse the list for multiple calls")
+	}
+	l.previousList = list
+
+	podList, ok := list.(*corev1.PodList)
+	if !ok {
+		return fmt.Errorf("expected *corev1.PodList, got %T", list)
+	}
+
+	listOptions := &client.ListOptions{}
+	listOptions.ApplyOptions(opts)
+
+	if l.calls > 1 {
+		if listOptions.Raw.ResourceVersion != "" {
+			return fmt.Errorf("the pager should reset the resourceVersion field for consecutive calls")
+		}
+		if listOptions.Raw.ResourceVersionMatch != "" {
+			return fmt.Errorf("the pager should reset the resourceVersionMatch field for consecutive calls")
+		}
+	}
+
+	limit := listOptions.Limit
+	if limit == 0 {
+		return fmt.Errorf("the pager should set limit")
+	}
+
+	var offset int64
+	if listOptions.Continue != "" {
+		var err error
+		offset, err = strconv.ParseInt(listOptions.Continue, 10, 64)
+		if err != nil {
+			return err
+		}
+	}
+
+	defer func() {
+		if offset+limit >= int64(len(l.allPods)) {
+			podList.Continue = ""
+		} else {
+			podList.Continue = strconv.FormatInt(offset+int64(len(podList.Items)), 10)
+		}
+	}()
+
+	podList.Items = l.allPods[offset:min(int64(len(l.allPods)), offset+limit)]
+	return nil
+}
+
+func podSlice(offset, n int64) []corev1.Pod {
+	pods := make([]corev1.Pod, n)
+
+	for i := int64(0); i < n; i++ {
+		pods[i] = corev1.Pod{ObjectMeta: metav1.ObjectMeta{Name: "pod-" + strconv.FormatInt(offset+i+1, 10)}}
+	}
+
+	return pods
+}
+
+func havePods(i, j int) gomegatypes.GomegaMatcher {
+	var matchers []any
+
+	for ; i <= j; i++ {
+		matchers = append(matchers, HaveName("pod-"+strconv.Itoa(i)))
+	}
+
+	return HaveExactElements(matchers...)
+}

pkg/utils/test/matchers/object.go

@@ -21,6 +21,11 @@ import (
 	gomegatypes "github.com/onsi/gomega/types"
 )
 
+// HaveName succeeds if the actual object has a matching name.
+func HaveName(name interface{}) gomegatypes.GomegaMatcher {
+	return HaveField("ObjectMeta.Name", name)
+}
+
 // HaveLabel succeeds if the actual object has a label with a matching key.
 func HaveLabel(key interface{}) gomegatypes.GomegaMatcher {
 	return HaveField("ObjectMeta.Labels", HaveKey(key))