for _, s := range spd {
				hdr.Size += s.Length
			}
			copy(blk.V7().Size(), zeroBlock[:]) // Reset field
			f.formatNumeric(blk.V7().Size(), hdr.Size)
			f.formatNumeric(blk.GNU().RealSize(), realSize)
		}
	*/
	blk.setFormat(FormatGNU)
	if err := tw.writeRawHeader(blk, hdr.Size, hdr.Typeflag); err != nil {
		return err
	}

	if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
		return nil, nil, err // EOF is okay here; exactly 0 bytes read
	}
	if bytes.Equal(tr.blk[:], zeroBlock[:]) {
		if _, err := io.ReadFull(tr.r, tr.blk[:]); err != nil {
			return nil, nil, err // EOF is okay here; exactly 1 block of zeros read
		}
		if bytes.Equal(tr.blk[:], zeroBlock[:]) {

			t.Errorf("test %d, unexpected Close error: %v", i, err)
		}

		// The prefix field should never appear in the GNU format.
		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)