Can anyone please tell me how to create a million blocks in regtest or testnet mode? Is there a way other than to start mining with the smallest difficulty?
Creating a private testnet and setting the difficulty very low is an easy way. You can start your testnet nodes passing the flag --fixed-difficulty N (where N is a very low number), so your mining node mines blocks near instantly.
There is also a new RPC command generateblocks, that can generate a bunch of blocks in regtest mode. It's currently not documented, but see the commit message. To use it, you would start monerod with the --regtest flag and the --fixed-difficulty flag (as detailed above). Then you can call the RPC interface passing the parameters: amount_of_blocks and wallet_address. For example:
curl -X POST http://127.0.0.1:18081/json_rpc -d
'{"jsonrpc":"2.0","id":"0","method":"generateblocks","params":{
"wallet_address":"44GBHzv...","amount_of_blocks":1000000}}'
-H 'Content-Type: application/json'
