HashPack supports testnet accounts. Testnet accounts are used to test out the Hedera network using “play” HBAR. The HBAR on testnet has no monetary value. In order to import or create a testnet account, select the testnet option in the appropriate account creation/import screen.
Note that testnet and mainnet accounts are on completely different networks and cannot interact with each other. If you accidentally send funds from a mainnet account to a testnet account you will lose your funds as you are actually sending the HBAR to an address that also happens to exist on mainnet.