I am designing user interface having both Ethereum mainnet and testnet addresses. Is it possible for the user to accidentally give testnet address when withdrawing in mainnet and vice versa?
How can I verify an address belongs to a particular Ethereum network?
Yes, it is possible for a user to withdraw funds to the testnet address on the mainnet. There is no way to verify if an address belongs to a particular network - they are all valid for every Ethereum network (it is just an address space from 0 to 2^160).
If you accidentally sent ether to the testnet address on the main network, you could quite easily get it because you would hold the private key for that address (a private key and public address pair would be the same on either network).
