etcd-io__etcd/raft/log_test.go

/*
   Copyright 2014 CoreOS, Inc.

   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 raft

import (
	"reflect"
	"testing"

	pb "github.com/coreos/etcd/raft/raftpb"
)

func TestFindConflict(t *testing.T) {
	previousEnts := []pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 3}}
	tests := []struct {
		ents      []pb.Entry
		wconflict uint64
	}{
		// no conflict, empty ent
		{[]pb.Entry{}, 0},
		{[]pb.Entry{}, 0},
		// no conflict
		{[]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 3}}, 0},
		{[]pb.Entry{{Index: 2, Term: 2}, {Index: 3, Term: 3}}, 0},
		{[]pb.Entry{{Index: 3, Term: 3}}, 0},
		// no conflict, but has new entries
		{[]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 3}, {Index: 4, Term: 4}, {Index: 5, Term: 4}}, 4},
		{[]pb.Entry{{Index: 2, Term: 2}, {Index: 3, Term: 3}, {Index: 4, Term: 4}, {Index: 5, Term: 4}}, 4},
		{[]pb.Entry{{Index: 3, Term: 3}, {Index: 4, Term: 4}, {Index: 5, Term: 4}}, 4},
		{[]pb.Entry{{Index: 4, Term: 4}, {Index: 5, Term: 4}}, 4},
		// conflicts with existing entries
		{[]pb.Entry{{Index: 1, Term: 4}, {Index: 2, Term: 4}}, 1},
		{[]pb.Entry{{Index: 2, Term: 1}, {Index: 3, Term: 4}, {Index: 4, Term: 4}}, 2},
		{[]pb.Entry{{Index: 3, Term: 1}, {Index: 4, Term: 2}, {Index: 5, Term: 4}, {Index: 6, Term: 4}}, 3},
	}

	for i, tt := range tests {
		raftLog := newLog(NewMemoryStorage())
		raftLog.append(previousEnts...)

		gconflict := raftLog.findConflict(tt.ents)
		if gconflict != tt.wconflict {
			t.Errorf("#%d: conflict = %d, want %d", i, gconflict, tt.wconflict)
		}
	}
}

func TestIsUpToDate(t *testing.T) {
	previousEnts := []pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 3}}
	raftLog := newLog(NewMemoryStorage())
	raftLog.append(previousEnts...)
	tests := []struct {
		lastIndex uint64
		term      uint64
		wUpToDate bool
	}{
		// greater term, ignore lastIndex
		{raftLog.lastIndex() - 1, 4, true},
		{raftLog.lastIndex(), 4, true},
		{raftLog.lastIndex() + 1, 4, true},
		// smaller term, ignore lastIndex
		{raftLog.lastIndex() - 1, 2, false},
		{raftLog.lastIndex(), 2, false},
		{raftLog.lastIndex() + 1, 2, false},
		// equal term, lager lastIndex wins
		{raftLog.lastIndex() - 1, 3, false},
		{raftLog.lastIndex(), 3, true},
		{raftLog.lastIndex() + 1, 3, true},
	}

	for i, tt := range tests {
		gUpToDate := raftLog.isUpToDate(tt.lastIndex, tt.term)
		if gUpToDate != tt.wUpToDate {
			t.Errorf("#%d: uptodate = %v, want %v", i, gUpToDate, tt.wUpToDate)
		}
	}
}

func TestAppend(t *testing.T) {
	previousEnts := []pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}}
	tests := []struct {
		ents      []pb.Entry
		windex    uint64
		wents     []pb.Entry
		wunstable uint64
	}{
		{
			[]pb.Entry{},
			2,
			[]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}},
			3,
		},
		{
			[]pb.Entry{{Index: 3, Term: 2}},
			3,
			[]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 2}},
			3,
		},
		// conflicts with index 1
		{
			[]pb.Entry{{Index: 1, Term: 2}},
			1,
			[]pb.Entry{{Index: 1, Term: 2}},
			1,
		},
		// conflicts with index 2
		{
			[]pb.Entry{{Index: 2, Term: 3}, {Index: 3, Term: 3}},
			3,
			[]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 3}, {Index: 3, Term: 3}},
			2,
		},
	}

	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.Append(previousEnts)
		raftLog := newLog(storage)

		index := raftLog.append(tt.ents...)
		if index != tt.windex {
			t.Errorf("#%d: lastIndex = %d, want %d", i, index, tt.windex)
		}
		if g := raftLog.entries(1); !reflect.DeepEqual(g, tt.wents) {
			t.Errorf("#%d: logEnts = %+v, want %+v", i, g, tt.wents)
		}
		if g := raftLog.unstable.offset; g != tt.wunstable {
			t.Errorf("#%d: unstable = %d, want %d", i, g, tt.wunstable)
		}
	}
}

// TestLogMaybeAppend ensures:
// If the given (index, term) matches with the existing log:
// 	1. If an existing entry conflicts with a new one (same index
// 	but different terms), delete the existing entry and all that
// 	follow it
// 	2.Append any new entries not already in the log
// If the given (index, term) does not match with the existing log:
// 	return false
func TestLogMaybeAppend(t *testing.T) {
	previousEnts := []pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}, {Index: 3, Term: 3}}
	lastindex := uint64(3)
	lastterm := uint64(3)
	commit := uint64(1)

	tests := []struct {
		logTerm   uint64
		index     uint64
		committed uint64
		ents      []pb.Entry

		wlasti  uint64
		wappend bool
		wcommit uint64
		wpanic  bool
	}{
		// not match: term is different
		{
			lastterm - 1, lastindex, lastindex, []pb.Entry{{Index: lastindex + 1, Term: 4}},
			0, false, commit, false,
		},
		// not match: index out of bound
		{
			lastterm, lastindex + 1, lastindex, []pb.Entry{{Index: lastindex + 2, Term: 4}},
			0, false, commit, false,
		},
		// match with the last existing entry
		{
			lastterm, lastindex, lastindex, nil,
			lastindex, true, lastindex, false,
		},
		{
			lastterm, lastindex, lastindex + 1, nil,
			lastindex, true, lastindex, false, // do not increase commit higher than lastnewi
		},
		{
			lastterm, lastindex, lastindex - 1, nil,
			lastindex, true, lastindex - 1, false, // commit up to the commit in the message
		},
		{
			lastterm, lastindex, 0, nil,
			lastindex, true, commit, false, // commit do not decrease
		},
		{
			0, 0, lastindex, nil,
			0, true, commit, false, // commit do not decrease
		},
		{
			lastterm, lastindex, lastindex, []pb.Entry{{Index: lastindex + 1, Term: 4}},
			lastindex + 1, true, lastindex, false,
		},
		{
			lastterm, lastindex, lastindex + 1, []pb.Entry{{Index: lastindex + 1, Term: 4}},
			lastindex + 1, true, lastindex + 1, false,
		},
		{
			lastterm, lastindex, lastindex + 2, []pb.Entry{{Index: lastindex + 1, Term: 4}},
			lastindex + 1, true, lastindex + 1, false, // do not increase commit higher than lastnewi
		},
		{
			lastterm, lastindex, lastindex + 2, []pb.Entry{{Index: lastindex + 1, Term: 4}, {Index: lastindex + 2, Term: 4}},
			lastindex + 2, true, lastindex + 2, false,
		},
		// match with the the entry in the middle
		{
			lastterm - 1, lastindex - 1, lastindex, []pb.Entry{{Index: lastindex, Term: 4}},
			lastindex, true, lastindex, false,
		},
		{
			lastterm - 2, lastindex - 2, lastindex, []pb.Entry{{Index: lastindex - 1, Term: 4}},
			lastindex - 1, true, lastindex - 1, false,
		},
		{
			lastterm - 3, lastindex - 3, lastindex, []pb.Entry{{Index: lastindex - 2, Term: 4}},
			lastindex - 2, true, lastindex - 2, true, // conflict with existing committed entry
		},
		{
			lastterm - 2, lastindex - 2, lastindex, []pb.Entry{{Index: lastindex - 1, Term: 4}, {Index: lastindex, Term: 4}},
			lastindex, true, lastindex, false,
		},
	}

	for i, tt := range tests {
		raftLog := newLog(NewMemoryStorage())
		raftLog.append(previousEnts...)
		raftLog.committed = commit
		func() {
			defer func() {
				if r := recover(); r != nil {
					if tt.wpanic != true {
						t.Errorf("%d: panic = %v, want %v", i, true, tt.wpanic)
					}
				}
			}()
			glasti, gappend := raftLog.maybeAppend(tt.index, tt.logTerm, tt.committed, tt.ents...)
			gcommit := raftLog.committed

			if glasti != tt.wlasti {
				t.Errorf("#%d: lastindex = %d, want %d", i, glasti, tt.wlasti)
			}
			if gappend != tt.wappend {
				t.Errorf("#%d: append = %v, want %v", i, gappend, tt.wappend)
			}
			if gcommit != tt.wcommit {
				t.Errorf("#%d: committed = %d, want %d", i, gcommit, tt.wcommit)
			}
			if gappend && len(tt.ents) != 0 {
				gents := raftLog.slice(raftLog.lastIndex()-uint64(len(tt.ents))+1, raftLog.lastIndex()+1)
				if !reflect.DeepEqual(tt.ents, gents) {
					t.Errorf("%d: appended entries = %v, want %v", i, gents, tt.ents)
				}
			}
		}()
	}
}

// TestCompactionSideEffects ensures that all the log related funcationality works correctly after
// a compaction.
func TestCompactionSideEffects(t *testing.T) {
	var i uint64
	// Populate the log with 1000 entries; 750 in stable storage and 250 in unstable.
	lastIndex := uint64(1000)
	unstableIndex := uint64(750)
	lastTerm := lastIndex
	storage := NewMemoryStorage()
	for i = 1; i <= unstableIndex; i++ {
		storage.Append([]pb.Entry{{Term: uint64(i), Index: uint64(i)}})
	}
	raftLog := newLog(storage)
	for i = unstableIndex; i < lastIndex; i++ {
		raftLog.append(pb.Entry{Term: uint64(i + 1), Index: uint64(i + 1)})
	}

	ok := raftLog.maybeCommit(lastIndex, lastTerm)
	if !ok {
		t.Fatalf("maybeCommit returned false")
	}
	raftLog.appliedTo(raftLog.committed)

	offset := uint64(500)
	storage.Compact(offset, nil, nil)

	if raftLog.lastIndex() != lastIndex {
		t.Errorf("lastIndex = %d, want %d", raftLog.lastIndex(), lastIndex)
	}

	for i := offset; i <= raftLog.lastIndex(); i++ {
		if raftLog.term(i) != i {
			t.Errorf("term(%d) = %d, want %d", i, raftLog.term(i), i)
		}
	}

	for i := offset; i <= raftLog.lastIndex(); i++ {
		if !raftLog.matchTerm(i, i) {
			t.Errorf("matchTerm(%d) = false, want true", i)
		}
	}

	unstableEnts := raftLog.unstableEntries()
	if g := len(unstableEnts); g != 250 {
		t.Errorf("len(unstableEntries) = %d, want = %d", g, 250)
	}
	if unstableEnts[0].Index != 751 {
		t.Errorf("Index = %d, want = %d", unstableEnts[0].Index, 751)
	}

	prev := raftLog.lastIndex()
	raftLog.append(pb.Entry{Index: raftLog.lastIndex() + 1, Term: raftLog.lastIndex() + 1})
	if raftLog.lastIndex() != prev+1 {
		t.Errorf("lastIndex = %d, want = %d", raftLog.lastIndex(), prev+1)
	}

	ents := raftLog.entries(raftLog.lastIndex())
	if len(ents) != 1 {
		t.Errorf("len(entries) = %d, want = %d", len(ents), 1)
	}
}

func TestNextEnts(t *testing.T) {
	snap := pb.Snapshot{
		Metadata: pb.SnapshotMetadata{Term: 1, Index: 3},
	}
	ents := []pb.Entry{
		{Term: 1, Index: 4},
		{Term: 1, Index: 5},
		{Term: 1, Index: 6},
	}
	tests := []struct {
		applied uint64
		wents   []pb.Entry
	}{
		{0, ents[:2]},
		{3, ents[:2]},
		{4, ents[1:2]},
		{5, nil},
	}
	for i, tt := range tests {
		storage := NewMemoryStorage()
		storage.ApplySnapshot(snap)
		raftLog := newLog(storage)
		raftLog.append(ents...)
		raftLog.maybeCommit(5, 1)
		raftLog.appliedTo(tt.applied)

		ents := raftLog.nextEnts()
		if !reflect.DeepEqual(ents, tt.wents) {
			t.Errorf("#%d: ents = %+v, want %+v", i, ents, tt.wents)
		}
	}
}

// TestUnstableEnts ensures unstableEntries returns the unstable part of the
// entries correctly.
func TestUnstableEnts(t *testing.T) {
	previousEnts := []pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}}
	tests := []struct {
		unstable uint64
		wents    []pb.Entry
	}{
		{3, nil},
		{1, previousEnts},
	}

	for i, tt := range tests {
		// append stable entries to storage
		storage := NewMemoryStorage()
		storage.Append(previousEnts[:tt.unstable-1])

		// append unstable entries to raftlog
		raftLog := newLog(storage)
		raftLog.append(previousEnts[tt.unstable-1:]...)

		ents := raftLog.unstableEntries()
		if l := len(ents); l > 0 {
			raftLog.stableTo(ents[l-1].Index, ents[l-i].Term)
		}
		if !reflect.DeepEqual(ents, tt.wents) {
			t.Errorf("#%d: unstableEnts = %+v, want %+v", i, ents, tt.wents)
		}
		w := previousEnts[len(previousEnts)-1].Index + 1
		if g := raftLog.unstable.offset; g != w {
			t.Errorf("#%d: unstable = %d, want %d", i, g, w)
		}
	}
}

func TestCommitTo(t *testing.T) {
	previousEnts := []pb.Entry{{Term: 1, Index: 1}, {Term: 2, Index: 2}, {Term: 3, Index: 3}}
	commit := uint64(2)
	tests := []struct {
		commit  uint64
		wcommit uint64
		wpanic  bool
	}{
		{3, 3, false},
		{1, 2, false}, // never decrease
		{4, 0, true},  // commit out of range -> panic
	}
	for i, tt := range tests {
		func() {
			defer func() {
				if r := recover(); r != nil {
					if tt.wpanic != true {
						t.Errorf("%d: panic = %v, want %v", i, true, tt.wpanic)
					}
				}
			}()
			raftLog := newLog(NewMemoryStorage())
			raftLog.append(previousEnts...)
			raftLog.committed = commit
			raftLog.commitTo(tt.commit)
			if raftLog.committed != tt.wcommit {
				t.Errorf("#%d: committed = %d, want %d", i, raftLog.committed, tt.wcommit)
			}
		}()
	}
}

func TestStableTo(t *testing.T) {
	tests := []struct {
		stablei   uint64
		stablet   uint64
		wunstable uint64
	}{
		{1, 1, 2},
		{2, 2, 3},
		{2, 1, 1}, // bad term
		{3, 1, 1}, // bad index
	}
	for i, tt := range tests {
		raftLog := newLog(NewMemoryStorage())
		raftLog.append([]pb.Entry{{Index: 1, Term: 1}, {Index: 2, Term: 2}}...)
		raftLog.stableTo(tt.stablei, tt.stablet)
		if raftLog.unstable.offset != tt.wunstable {
			t.Errorf("#%d: unstable = %d, want %d", i, raftLog.unstable.offset, tt.wunstable)
		}
	}
}

func TestStableToWithSnap(t *testing.T) {
	snapi, snapt := uint64(5), uint64(2)
	tests := []struct {
		stablei uint64
		stablet uint64
		newEnts []pb.Entry

		wunstable uint64
	}{
		{snapi + 1, snapt, nil, snapi + 1},
		{snapi, snapt, nil, snapi + 1},
		{snapi - 1, snapt, nil, snapi + 1},

		{snapi + 1, snapt + 1, nil, snapi + 1},
		{snapi, snapt + 1, nil, snapi + 1},
		{snapi - 1, snapt + 1, nil, snapi + 1},

		{snapi + 1, snapt, []pb.Entry{{Index: snapi + 1, Term: snapt}}, snapi + 2},
		{snapi, snapt, []pb.Entry{{Index: snapi + 1, Term: snapt}}, snapi + 1},
		{snapi - 1, snapt, []pb.Entry{{Index: snapi + 1, Term: snapt}}, snapi + 1},

		{snapi + 1, snapt + 1, []pb.Entry{{Index: snapi + 1, Term: snapt}}, snapi + 1},
		{snapi, snapt + 1, []pb.Entry{{Index: snapi + 1, Term: snapt}}, snapi + 1},
		{snapi - 1, snapt + 1, []pb.Entry{{Index: snapi + 1, Term: snapt}}, snapi + 1},
	}
	for i, tt := range tests {
		s := NewMemoryStorage()
		s.ApplySnapshot(pb.Snapshot{Metadata: pb.SnapshotMetadata{Index: snapi, Term: snapt}})
		raftLog := newLog(s)
		raftLog.append(tt.newEnts...)
		raftLog.stableTo(tt.stablei, tt.stablet)
		if raftLog.unstable.offset != tt.wunstable {
			t.Errorf("#%d: unstable = %d, want %d", i, raftLog.unstable.offset, tt.wunstable)
		}
	}
}

//TestCompaction ensures that the number of log entries is correct after compactions.
func TestCompaction(t *testing.T) {
	tests := []struct {
		lastIndex uint64
		compact   []uint64
		wleft     []int
		wallow    bool
	}{
		// out of upper bound
		{1000, []uint64{1001}, []int{-1}, false},
		{1000, []uint64{300, 500, 800, 900}, []int{700, 500, 200, 100}, true},
		// out of lower bound
		{1000, []uint64{300, 299}, []int{700, -1}, false},
	}

	for i, tt := range tests {
		func() {
			defer func() {
				if r := recover(); r != nil {
					if tt.wallow == true {
						t.Errorf("%d: allow = %v, want %v: %v", i, false, true, r)
					}
				}
			}()

			storage := NewMemoryStorage()
			for i := uint64(1); i <= tt.lastIndex; i++ {
				storage.Append([]pb.Entry{{Index: i}})
			}
			raftLog := newLog(storage)
			raftLog.maybeCommit(tt.lastIndex, 0)
			raftLog.appliedTo(raftLog.committed)

			for j := 0; j < len(tt.compact); j++ {
				err := storage.Compact(tt.compact[j], nil, nil)
				if err != nil {
					if tt.wallow {
						t.Errorf("#%d.%d allow = %t, want %t", i, j, false, tt.wallow)
					}
					continue
				}
				if len(raftLog.allEntries()) != tt.wleft[j] {
					t.Errorf("#%d.%d len = %d, want %d", i, j, len(raftLog.allEntries()), tt.wleft[j])
				}
			}
		}()
	}
}

func TestLogRestore(t *testing.T) {
	index := uint64(1000)
	term := uint64(1000)
	snap := pb.SnapshotMetadata{Index: index, Term: term}
	storage := NewMemoryStorage()
	storage.ApplySnapshot(pb.Snapshot{Metadata: snap})
	raftLog := newLog(storage)

	if len(raftLog.allEntries()) != 0 {
		t.Errorf("len = %d, want 0", len(raftLog.allEntries()))
	}
	if raftLog.firstIndex() != index+1 {
		t.Errorf("firstIndex = %d, want %d", raftLog.firstIndex(), index+1)
	}
	if raftLog.committed != index {
		t.Errorf("committed = %d, want %d", raftLog.committed, index)
	}
	if raftLog.unstable.offset != index+1 {
		t.Errorf("unstable = %d, want %d", raftLog.unstable, index+1)
	}
	if raftLog.term(index) != term {
		t.Errorf("term = %d, want %d", raftLog.term(index), term)
	}
}

func TestIsOutOfBounds(t *testing.T) {
	offset := uint64(100)
	num := uint64(100)
	storage := NewMemoryStorage()
	storage.ApplySnapshot(pb.Snapshot{Metadata: pb.SnapshotMetadata{Index: offset}})
	l := newLog(storage)
	for i := uint64(1); i <= num; i++ {
		l.append(pb.Entry{Index: i + offset})
	}

	first := offset + 1
	tests := []struct {
		lo, hi uint64
		wpainc bool
	}{
		{
			first - 2, first + 1,
			true,
		},
		{
			first - 1, first + 1,
			true,
		},
		{
			first, first,
			false,
		},
		{
			first + num/2, first + num/2,
			false,
		},
		{
			first + num - 1, first + num - 1,
			false,
		},
		{
			first + num, first + num,
			false,
		},
		{
			first + num, first + num + 1,
			true,
		},
		{
			first + num + 1, first + num + 1,
			true,
		},
	}

	for i, tt := range tests {
		func() {
			defer func() {
				if r := recover(); r != nil {
					if !tt.wpainc {
						t.Errorf("%d: panic = %v, want %v: %v", i, true, false, r)
					}
				}
			}()
			l.mustCheckOutOfBounds(tt.lo, tt.hi)
			if tt.wpainc {
				t.Errorf("%d: panic = %v, want %v", i, false, true)
			}
		}()
	}
}

func TestTerm(t *testing.T) {
	var i uint64
	offset := uint64(100)
	num := uint64(100)

	storage := NewMemoryStorage()
	storage.ApplySnapshot(pb.Snapshot{Metadata: pb.SnapshotMetadata{Index: offset, Term: 1}})
	l := newLog(storage)
	for i = 1; i < num; i++ {
		l.append(pb.Entry{Index: offset + i, Term: i})
	}

	tests := []struct {
		index uint64
		w     uint64
	}{
		{offset - 1, 0},
		{offset, 1},
		{offset + num/2, num / 2},
		{offset + num - 1, num - 1},
		{offset + num, 0},
	}

	for i, tt := range tests {
		term := l.term(tt.index)
		if !reflect.DeepEqual(term, tt.w) {
			t.Errorf("#%d: at = %d, want %d", i, term, tt.w)
		}
	}
}

func TestTermWithUnstableSnapshot(t *testing.T) {
	storagesnapi := uint64(100)
	unstablesnapi := storagesnapi + 5

	storage := NewMemoryStorage()
	storage.ApplySnapshot(pb.Snapshot{Metadata: pb.SnapshotMetadata{Index: storagesnapi, Term: 1}})
	l := newLog(storage)
	l.restore(pb.Snapshot{Metadata: pb.SnapshotMetadata{Index: unstablesnapi, Term: 1}})

	tests := []struct {
		index uint64
		w     uint64
	}{
		// cannot get term from storage
		{storagesnapi, 0},
		// cannot get term from the gap between storage ents and unstable snapshot
		{storagesnapi + 1, 0},
		{unstablesnapi - 1, 0},
		// get term from unstable snapshot index
		{unstablesnapi, 1},
	}

	for i, tt := range tests {
		term := l.term(tt.index)
		if !reflect.DeepEqual(term, tt.w) {
			t.Errorf("#%d: at = %d, want %d", i, term, tt.w)
		}
	}
}

func TestSlice(t *testing.T) {
	var i uint64
	offset := uint64(100)
	num := uint64(100)

	storage := NewMemoryStorage()
	storage.ApplySnapshot(pb.Snapshot{Metadata: pb.SnapshotMetadata{Index: offset}})
	l := newLog(storage)
	for i = 1; i < num; i++ {
		l.append(pb.Entry{Index: offset + i, Term: offset + i})
	}

	tests := []struct {
		from   uint64
		to     uint64
		w      []pb.Entry
		wpanic bool
	}{
		{offset - 1, offset + 1, nil, true},
		{offset, offset + 1, nil, true},
		{offset + num/2, offset + num/2 + 1, []pb.Entry{{Index: offset + num/2, Term: offset + num/2}}, false},
		{offset + num - 1, offset + num, []pb.Entry{{Index: offset + num - 1, Term: offset + num - 1}}, false},
		{offset + num, offset + num + 1, nil, true},
	}

	for i, tt := range tests {
		func() {
			defer func() {
				if r := recover(); r != nil {
					if !tt.wpanic {
						t.Errorf("%d: panic = %v, want %v: %v", i, true, false, r)
					}
				}
			}()
			g := l.slice(tt.from, tt.to)
			if !reflect.DeepEqual(g, tt.w) {
				t.Errorf("#%d: from %d to %d = %v, want %v", i, tt.from, tt.to, g, tt.w)
			}
		}()
	}
}