// Write the initial GNU header.
		var blk block
		gnu := blk.toGNU()
		sparse := gnu.sparse()
		copy(gnu.realSize(), size)
		sps = populateSparseMap(sparse, sps)
		if format != FormatUnknown {
			blk.setFormat(format)
		}
		out = append(out, blk[:]...)

		// Write extended sparse blocks.
		for len(sps) > 0 {
			var blk block
			sps = populateSparseMap(blk.toSparse(), sps)
			out = append(out, blk[:]...)

            return "HmacMD5";
          }

          @Override
          public byte[] getEncoded() {
            return new byte[8];
          }

          @Override
          public String getFormat() {
            return "RAW";
          }
        };
    assertThat(
            hmacMd5(customKey)
                .hashString("The quick brown fox jumps over the lazy dog", UTF_8)