is there an ecash testnet?
there is, but I don't believe in testnet
https://image.nostr.build/4d9ae032f9310ac3fe1d007e8c4e16aa96404b47b12f1cf7698ed4e13412282b.jpg
No. There are test mints that let you mint for free but you can do the same in real mints. There is no chain, custodian (trusted third party that issues ecash) decides the rules.