A lot of people use polar to test lightning applications and help handle the question you are asking.  You can learn more here:  https://lightningpolar.com/

Thanks! I believe in regtest I would have to set up the network right? 
In signet, I have seen there are lightning nodes already. Is there a way to get coins? Is there a faucet or a way to mine with cpu?

Notfast

ChrisS

mempool

I have seen that mempool in testnet is very large (testnet 3) despite that blocks are being confirmed a lot (less than 1 minute per block). The same applies for testnet 4. Is fast block confirmation a problem for lightning network in those networks? In the past I used to experiment an application using testnet lightning but since "storms" started my node desynced. I wonder where can I develop in lightning (other than the mainnet)