pilorama: Add tricky test for SortedByFilename

Signed-off-by: Evgenii Stratonikov <e.stratonikov@yadro.com>

pkg/local_object_storage/pilorama/forest_test.go

@@ -1,11 +1,13 @@
 package pilorama
 
 import (
+	"bytes"
 	"context"
 	"crypto/rand"
 	"fmt"
 	mrand "math/rand"
 	"path/filepath"
+	"slices"
 	"strconv"
 	"strings"
 	"sync"
@@ -232,6 +234,66 @@ func BenchmarkForestSortedIteration(b *testing.B) {
 	}
 }
 
+// The issue which we call "BugWithSkip" is easiest to understand when filenames are
+// monotonically increasing numbers. We want the list of sorted filenames to have different length interleaved.
+// The bug happens when we switch between length during listing.
+// Thus this test contains numbers from 1 to 1000 and batch size of size 100.
+func TestForest_TreeSortedIterationBugWithSkip(t *testing.T) {
+	t.Skip()
+	for i := range providers {
+		t.Run(providers[i].name, func(t *testing.T) {
+			testForestTreeSortedIterationBugWithSkip(t, providers[i].construct(t))
+		})
+	}
+}
+
+func testForestTreeSortedIterationBugWithSkip(t *testing.T, s ForestStorage) {
+	defer func() { require.NoError(t, s.Close()) }()
+
+	cid := cidtest.ID()
+	d := CIDDescriptor{cid, 0, 1}
+	treeID := "version"
+	treeAdd := func(t *testing.T, ts int, filename string) {
+		_, err := s.TreeMove(context.Background(), d, treeID, &Move{
+			Child:  RootID + uint64(ts),
+			Parent: RootID,
+			Meta: Meta{
+				Time: Timestamp(ts),
+				Items: []KeyValue{
+					{Key: AttributeFilename, Value: []byte(filename)},
+				},
+			},
+		})
+		require.NoError(t, err)
+	}
+
+	const count = 2000
+	treeAdd(t, 1, "")
+	for i := 1; i < count; i++ {
+		treeAdd(t, i+1, strconv.Itoa(i+1))
+	}
+
+	var result []MultiNodeInfo
+	treeAppend := func(t *testing.T, last *string, count int) *string {
+		res, cursor, err := s.TreeSortedByFilename(context.Background(), d.CID, treeID, MultiNode{RootID}, last, count)
+		require.NoError(t, err)
+		result = append(result, res...)
+		return cursor
+	}
+
+	const batchSize = 10
+	last := treeAppend(t, nil, batchSize)
+	for i := 1; i < count/batchSize; i++ {
+		last = treeAppend(t, last, batchSize)
+	}
+	require.Len(t, result, count)
+	require.True(t, slices.IsSortedFunc(result, func(a, b MultiNodeInfo) int {
+		filenameA := findAttr(a.Meta, AttributeFilename)
+		filenameB := findAttr(b.Meta, AttributeFilename)
+		return bytes.Compare(filenameA, filenameB)
+	}))
+}
+
 func TestForest_TreeSortedIteration(t *testing.T) {
 	for i := range providers {
 		t.Run(providers[i].name, func(t *testing.T) {