Add preallocate tests

internal/restorer/preallocate_test.go

@@ -0,0 +1,34 @@
+package restorer
+
+import (
+	"os"
+	"path"
+	"strconv"
+	"testing"
+
+	"github.com/restic/restic/internal/fs"
+	"github.com/restic/restic/internal/test"
+)
+
+func TestPreallocate(t *testing.T) {
+	for _, i := range []int64{0, 1, 4096, 1024 * 1024} {
+		t.Run(strconv.FormatInt(i, 10), func(t *testing.T) {
+			dirpath, cleanup := test.TempDir(t)
+			defer cleanup()
+
+			flags := os.O_CREATE | os.O_TRUNC | os.O_WRONLY
+			wr, err := os.OpenFile(path.Join(dirpath, "test"), flags, 0600)
+			test.OK(t, err)
+			defer wr.Close()
+
+			err = preallocateFile(wr, i)
+			test.OK(t, err)
+
+			fi, err := wr.Stat()
+			test.OK(t, err)
+
+			efi := fs.ExtendedStat(fi)
+			test.Assert(t, efi.Size == i || efi.Blocks > 0, "Preallocated size of %v, got size %v block %v", i, efi.Size, efi.Blocks)
+		})
+	}
+}