A test net is a network where a cryptocurrency is tested before it becomes available to the public.

Before a currency switches to its own mainnet, all functionalities are tested. The functionalities are tested on a so-called "testnet. Each network also has its own testnet, at Ethereum this is Goerli. When a new coin or token is created on the Ethereum network, it is first tested on the Goerli network. Testing is often done by developers themselves and, unlike the mainnet, is not open to the public. When everything works as it should, the testnet is transferred to a mainnet. Incidentally, the testnet often continues to exist. In case of updates, testing can then be done on the testnet first. Errors then have no major consequences and can easily be adjusted

In addition to security, a test net also has the advantage of being cheaper. This is because a fee must be paid for each transaction on a blockchain. With a testnet this is not necessary, so unlimited testing can be done without costing money.