user114696: If I have valid private key to use on Bitcoin mainnet, can I use the same key to generate addresses and spend on testnet? If so, is this encouraged, or should one generally keep separate keys to use on mainnet and testnet?

user109558: Yes. A valid private key can be used either on testnet and mainnet. But key reuse is never a good thing, even within the same chain. Just use two different wallets, it's free!

114696: <p>If I have valid private key to use on Bitcoin mainnet, can I use the same key to generate addresses and spend on testnet? If so, is this encouraged, or should one generally keep separate keys to use on mainnet and testnet?</p>
 109558: <p>Yes. A valid private key can be used either on testnet and mainnet. But key reuse is never a good thing, even within the same chain. Just use two different wallets, it's free!</p>
