Mycelium Perpetual Pools are available on the Arbitrum Rinkeby testnet.
You can switch Perpetual Pools to testnet mode by clicking the network selector in the top right corner next to your wallet address and choosing Arbitrum Rinkeby. You will be prompted to confirm the network change after which you are now using a testnet instance of the Perpetual Pools.
You can get PPUSD, the Settlement Asset used in the testnet Pools, via our Discord. On the #get-test-tokens channel, type in the command
!claimfollowed by your address to claim PPUSD. You will also need testnet ETH to perform actions.