var blk block
		copy(blk[:], b.Bytes())
		prefix := string(blk.toUSTAR().prefix())
		prefix, _, _ = strings.Cut(prefix, "\x00") // Truncate at the NUL terminator
		if blk.getFormat() == FormatGNU && len(prefix) > 0 && strings.HasPrefix(name, prefix) {
			t.Errorf("test %d, found prefix in GNU format: %s", i, prefix)
		}

		tr := NewReader(&b)
		hdr, err := tr.Next()