You open your testnet wallet, go to send tab, enter the receiver's testnet address, enter an amount and click send.
Hello
Can you please tell me what is testnet wallet, i saw (testnet application + bitcoin wallet application) in Android !?
As NotATether said, bitcoin core has the option to work with testnet.
Also, electrum does also (./electrum --testnet).
I haven't tried any other wallets besides those two (yet).
Jim