The testnet runs on the Monero stagenet and Ethereum Kovan testnet. To participate you need
a few things.
Next you need to create a Monero stagenet wallet:
monero-wallet-cli --stagenet --daemon-host stagenet.community.xmr.to
Follow the prompts to create a stagenet wallet and connect to the xmr.to public node.
Open metamask and create a new wallet.
Switch to the Kovan testnet
Add the WXMR token as a custom token using the contract address 0xa15de64076298899c09fa9aa3d1e25a2a10651f7
Finally, you need some coins to swap.
XMR stagenet faucet
Kovan ETH faucet
After following these steps you will have the wallets you need, charged with coins ready to