The generate RPC nearly instantly generates blocks.
generate nblocks ( maxtries )
*bitcoin-cli help generate
generate nblocks ( maxtries ) Mine up to nblocks blocks immediately (before the RPC call returns) to an address in the wallet. Arguments: 1. nblocks (numeric, required) How many blocks are generated immediately. 2. maxtries (numeric, optional) How many iterations to try (default = 1000000). Result: [ blockhashes ] (array) hashes of blocks generated Examples: Generate 11 blocks > bitcoin-cli generate 11