Testnet is a trial. If you see testnet, then you are in test mode. This illustrates the mainnet mode will also work according to the ongoing testnet mode. This is not much different from the beta.
If you create an app, before officially launching it to the public, then you must launch the beta version of the app as a feasibility test.
Likewise on the Ethereum blockchain. Before the official version of the token is released to the public, a testnet version will be developed as a trial.
Exactly, every app released testnet version for blockchain network testing and even project team will reward anyone who use testnet feature will be given token/coin reward, some testnet even worth more than $100+ for each user and but we have to make sure to join the program testnet of popular projects.