To trade on Testnet, you will need Testnet coins. They are the testing version of each cryptocurrency that has no monetary value. Testnet Bitcoin is freely distributed from a number of faucets around the internet. 100,000 Testnet Tether (USDT_T2) will be credited once a USDT deposit address is created in Testnet. You can trade on your BitMEX Testnet account using these coins with no risk of actual monetary profit or loss.