add freelist interface unit tests

Signed-off-by: Thomas Jungblut <tjungblu@redhat.com>

internal/freelist/array_test.go

@@ -4,6 +4,8 @@ import (
 	"reflect"
 	"testing"
 
+	"github.com/stretchr/testify/require"
+
 	"go.etcd.io/bbolt/internal/common"
 )
 
@@ -50,3 +52,12 @@ func TestFreelistArray_allocate(t *testing.T) {
 		t.Fatalf("exp=%v; got=%v", exp, f.freePageIds())
 	}
 }
+
+func TestInvalidArrayAllocation(t *testing.T) {
+	f := NewArrayFreelist()
+	ids := []common.Pgid{1}
+	f.Init(ids)
+	require.Panics(t, func() {
+		f.Allocate(common.Txid(1), 1)
+	})
+}

internal/freelist/freelist.go

@@ -53,6 +53,7 @@ type Interface interface {
 	Freed(pgId common.Pgid) bool
 
 	// Rollback removes the pages from a given pending tx.
+	// Should always be followed by Reload or NoSyncReload from last freelist state.
 	Rollback(txId common.Txid)
 
 	// Copyall copies a list of all free ids and all pending ids in one sorted list.