switch maker := v.maker.(type) {
		case makeReg:
			fw = &regFileWriter{w, maker.size}
			wantStr = maker.wantStr
		case makeSparse:
			if !validateSparseEntries(maker.sph, maker.size) {
				t.Fatalf("invalid sparse map: %v", maker.sph)
			}
			spd := invertSparseEntries(maker.sph, maker.size)
			fw = &regFileWriter{w, maker.makeReg.size}
			fw = &sparseFileWriter{fw, spd, 0}
			wantStr = maker.makeReg.wantStr

	// write a zip file
	archive := new(bytes.Buffer)
	w := NewWriter(archive)

	for i := range files {
		f := &files[i]
		f.crc32 = crc32.ChecksumIEEE(f.content)
		size := uint64(len(f.content))
		f.uncompressedSize = size
		f.compressedSize = size

		var compressedContent []byte
		if f.method == Deflate {
			var buf bytes.Buffer
			w, err := flate.NewWriter(&buf, flate.BestSpeed)
			if err != nil {