A testnet is what enables developers to simulate usage of the Hive blockchain for multiple purposes. It allows application developers to ensure that Hive-powered applications are functioning properly and blockchain developers to ensure that the blockchain itself is doing what the devs expect. That’s why having a testnet better is a great way of improving the entire ecosystem.
But since Hive is not a centralized project, neither is the testnet. In fact, there are multiple testnets with different goals. My goal is to mirror accounts and balances in proportion to the mainnet, along with a sampling of current mainnet activity:
testnet: true
majority version: 1.25.0
p2p: 134.209.41.170:2001
rpc: http://134.209.41.170:8091
chain-id: 18dcf0a285365fc58b71f18b3d3fec954aa0c141c44e4e5cb4cf777b9eab274e
This is accomplished using tinman. If you're developing an app and want to try it out on my testnet, just use your mainnet credentials. Ideally, witnesses would also run their own nodes on this testnet as well.
If you want to set up your own testnet like I did, I've also updated the tutorial on the devportal: Setting Up a Testnet
Also see: Hard fork 24 node setup by 
'Automating' comes from the roots 'auto-' meaning 'self-', and 'mating', meaning 'screwing'.