Why would you want to write your own miner? There is open-source CPU, GPU and ASIC miner software for almost everything (and that you can adapt to your hardware if unsupported).

Recent topics about Bitcoin mining setup on Testnet.
bfgminer (CPU, GPU): https://bitcointalk.org/index.php?topic=5415861.0
cgminer (ASIC): https://bitcointalk.org/index.php?topic=5415335.0