readers[i] = newMetacacheReader(r)
		d := disks[i]

		// Send request to each disk.
		go func() {
			var werr error
			if d == nil {
				werr = errDiskNotFound
			} else {
				werr = d.WalkDir(ctx, WalkDirOptions{
					Limit:          opts.perDiskLimit,
					Bucket:         opts.bucket,
					BaseDir:        opts.path,
					Recursive:      opts.recursive,
					ReportNotFound: opts.reportNotFound,

			var files []string
			sawErr := false
			err = fs.WalkDir(z, ".", func(path string, d fs.DirEntry, err error) error {
				if err != nil {
					if !test.wantErr {
						t.Errorf("%s: %v", path, err)
					}
					sawErr = true
					return nil
				}
				files = append(files, path)
				return nil
			})
			if err != nil {
				t.Errorf("fs.WalkDir error: %v", err)
			}
			if test.wantErr && !sawErr {