fix ut

Signed-off-by: Yifan Yuan <tuji.yyf@alibaba-inc.com>

Author: BigVan

pkg/snapshot/overlay_test.go

@@ -28,6 +28,7 @@ import (
 func newSnapshotterWithOpts(opts ...Opt) testsuite.SnapshotterFunc {
 	return func(ctx context.Context, root string) (snapshots.Snapshotter, func() error, error) {
 		cfg := DefaultBootConfig()
+		cfg.Root = root
 		snapshotter, err := NewSnapshotter(cfg, opts...)
 		if err != nil {
 			return nil, nil, err